Liquid jetting device and liquid jetting method

ABSTRACT

The number of liquid droplets ejected toward a region outside a medium, which becomes a necessary evil when forming dots all the way to the edges of the medium by ejecting liquid droplets, can be decreased without greatly impairing the formation of dots at the edges. A liquid ejection apparatus for ejecting a liquid, includes: a liquid ejection section for ejecting liquid droplets toward a medium in order to form dots on the medium; wherein the liquid ejection section ejects, toward a vicinity of an edge of the medium, the liquid droplets of a number that has been thinned out by a suitable number; and wherein at least a portion of the liquid droplets ejected after thinning does not land on the medium.

TECHNICAL FIELD

The present invention relates to liquid ejection apparatuses and liquidejection methods forming dots on a medium by ejecting liquid dropletsonto that medium.

BACKGROUND ART

Inkjet printers are known as one type of liquid ejection apparatus forejecting droplets of a liquid toward a medium. Such inkjet printerseject droplets of ink, as the liquid droplets, toward print paper(hereinafter also referred to as paper) serving as a medium to form amultitude dots on the print paper, thereby printing a macroscopic imagewith these dots.

Such inkjet printers are provided with a print function known as“borderless printing.” This is the function of printing an image onpaper without forming margins by forming dots over the entire paper upto its edges. Ordinarily, by using image data that is larger in sizethan the paper, liquid droplets are ejected toward regions outside thepaper so that there are no areas at the edges in which, unintentionally,no dots are formed due to, for example, the position of the paper beingmisaligned during carrying.

However, almost all of the liquid droplets that are ejected to thisoutside area are abandoned without forming dots on the paper, leading toan increased amount of ink that is used.

In view of these circumstances, it is an object of the present inventionto achieve a liquid ejection apparatus and a liquid ejection method withwhich the number of liquid droplets ejected toward the region outsidethe medium, which becomes a necessary evil when trying to form dots allthe way to the edges of the medium by ejecting liquid droplets, can bedecreased without greatly impairing the formation of dots at the edges.

DISCLOSURE OF INVENTION

In order to address the above issue, a primary aspect of the presentinvention is a liquid ejection apparatus for ejecting a liquid,comprising: a liquid ejection section for ejecting liquid dropletstoward a medium in order to form dots on the medium; wherein the liquidejection section ejects, toward a vicinity of an edge of the medium, theliquid droplets of a number that has been thinned out by a suitablenumber; and wherein at least a portion of the liquid droplets ejectedafter thinning does not land on the medium.

Another primary aspect of the present invention is a liquid ejectionmethod for ejecting liquid droplets toward a medium in order to formdots on the medium, comprising: a step of thinning out a suitable numberof liquid droplets to be ejected; and a step of ejecting, toward avicinity of an edge of the medium, the liquid droplets of a number thathas been thinned out by the suitable number; wherein at least a portionof the liquid droplets ejected after thinning does not land on themedium.

Features and objects of the present invention other than the above willbecome clear through the present specification with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing an embodiment of an inkjet printer1.

FIG. 2 is an explanatory diagram of the overall configuration of theinkjet printer 1.

FIG. 3 is a diagram showing a carriage 41 etc. of the inkjet printer 1.

FIG. 4 is a diagram showing the carrying mechanism of the inkjet printer1.

FIG. 5 is an explanatory diagram showing the arrangement of the nozzlesin the head 21.

FIG. 6 is a block diagram showing the configuration within the drivecircuit.

FIG. 7 is an explanatory diagram illustrating the processing on the hostside.

FIG. 8A is an explanatory diagram of ordinary interlaced printing.

FIG. 8B is an explanatory diagram of ordinary interlaced printing.

FIG. 9A is an explanatory diagram of ordinary overlap printing.

FIG. 9B is an explanatory diagram of ordinary overlap printing.

FIG. 10 is an explanatory diagram illustrating the relationship betweenthe size of the print region A and the paper S during ordinary printing.

FIG. 11 is an explanatory diagram illustrating the relationship betweenthe size of the print region A and the paper S during borderlessprinting.

FIG. 12 is a plan view showing an ink collection section 80.

FIG. 13A is a cross-sectional view showing a first ink collectionsection 82.

FIG. 13B is a cross-sectional view showing a first ink collectionsection 82.

FIG. 14 is a cross-sectional view showing a second ink collectionsection 83.

FIG. 15A is a plan view conceptually showing the thinned-out state.

FIG. 15B is a plan view conceptually showing the thinned-out state.

FIG. 15C is a flowchart of the thinning processing section 224.

FIG. 16 is an explanatory diagram showing an example of the thinningprocess during interlaced printing.

FIG. 17 is an explanatory diagram showing an example of the thinningprocess during interlaced printing.

FIG. 18 is an explanatory diagram showing an example of the thinningprocess during interlaced printing.

FIG. 19 is an explanatory diagram showing an example of the thinningprocess during interlaced printing.

FIG. 20 is an explanatory diagram showing an example of the thinningprocess during interlaced printing.

FIG. 21 is an explanatory diagram showing an example of the thinningprocess during interlaced printing.

FIG. 22 is an explanatory diagram showing an example of the thinningprocess during interlaced printing.

FIG. 23 is an explanatory diagram showing an example of the thinningprocess during interlaced printing.

FIG. 24 is an explanatory diagram showing an example of the thinningprocess during overlap printing.

FIG. 25 is an explanatory diagram showing an example of the thinningprocess during overlap printing.

FIG. 26 is an explanatory diagram showing an example of the thinningprocess during overlap printing.

FIG. 27 is an explanatory diagram showing an example of the thinningprocess during overlap printing.

FIG. 28 is an explanatory diagram showing an example of the thinningprocess during overlap printing.

FIG. 29 is an explanatory diagram showing an example of the thinningprocess during overlap printing.

FIG. 30 is an explanatory diagram showing an example of the thinningprocess during overlap printing.

FIG. 31 is an explanatory diagram showing an example of the thinningprocess during overlap printing.

FIG. 32 is a diagram used to find a preferable example of the changepattern.

FIG. 33 is a diagram used to find a preferable example of the changepattern.

FIG. 34 is a diagram used to find a preferable example of the changepattern.

FIG. 35 is a diagram used to find a preferable example of the changepattern.

FIG. 36 is a diagram used to find a preferable example of the changepattern.

A legend of the main reference numerals used in the drawings is shownbelow.

1 . . . inkjet printer/2 . . . control panel/3 . . . paper dischargesection/4 . . . paper supply section/5 . . . control buttons/6 . . .display lamps/7 . . . paper discharge tray/8 . . . paper supply tray/10. . . paper carry unit/13 . . . paper supply roller/14 . . . platen/15 .. . paper carry motor (PF motor)/16 . . . paper carry motor driver (PFmotor driver)/17A . . . carry roller/17B . . . paper dischargeroller/18A . . . free roller/18B . . . free roller/20 . . . ink ejectionunit/21 . . . ejection head/211 . . . nozzle row/22 . . . headdriver/221 . . . original drive signal generation section/222 . . . maskcircuits/223 . . . drive signal correction section/224 . . . thinningprocessing section/30 . . . cleaning unit/31 . . . pump device/32 . . .pump motor/33 . . . pump motor driver/35 . . . capping device/40 . . .carriage unit/41 . . . carriage/42 . . . carriage motor (CR motor)/43 .. . carriage motor driver (CR motor driver)/44 . . . pulley/45 . . .timing belt/46 . . . guide rail 150 . . . measuring instrument group/51. . . linear encoder/511 . . . linear scale/512 . . . detectionsection/512A . . . light-emitting diode/512B . . . collimator lens/512C. . . detection processing section/512D . . . photodiode/512E . . .signal processing circuit/512F . . . comparator/52 . . . rotaryencoder/53 . . . paper detection sensor 54 . . . paper width sensor/60 .. . control unit/61 . . . CPU/62 . . . timer/63 . . . interfacesection/64 . . . ASIC/65 . . . memory/66 . . . DC controller/67 . . .host computer/80 . . . ink collection section/82 . . . first inkcollection section/83 . . . second ink collection section/84 . . .absorbing material/90 . . . computer/91 . . . video driver/93 . . .display device/95 . . . application program/96 . . . printer driver/97 .. . resolution conversion module/98 . . . color conversion module/99 . .. halftone module/100 . . . rasterizer/101 . . . user interface displaymodule/102 . . . UI printer interface module/A . . . print region/As . .. reference region/Aa . . . abandonment region/S . . . medium (paper)/R. . . raster line

BEST MODE FOR CARRYING OUT THE INVENTION

At least the following matters will be made clear by the presentspecification and the accompanying drawings.

A liquid ejection apparatus for ejecting a liquid, comprises: a liquidejection section for ejecting liquid droplets toward a medium in orderto form dots on the medium; wherein the liquid ejection section ejects,toward a vicinity of an edge of the medium, the liquid droplets of anumber that has been thinned out by a suitable number; and wherein atleast a portion of the liquid droplets ejected after thinning does notland on the medium.

With this liquid ejection apparatus, a suitable number of the liquiddroplets are thinned out when ejecting those liquid droplets toward thevicinity of an edge of the medium. Consequently, it becomes possible toreduce the number of liquid droplets that do not land on the medium,which becomes a necessary evil when forming dots all the way to theedges of the medium, while substantially ensuring that the formation ofdots in the vicinity of the edges is not impaired.

In the liquid ejection apparatus, when ejecting the liquid droplets fromthe liquid ejection section toward a region that is determined to beoutside the medium, the liquid droplets may be ejected after thinning asuitable number of the liquid droplets that are to be ejected towardthat region.

With this liquid ejection apparatus, a suitable number of liquiddroplets are thinned out from the liquid droplets to be ejected towardthe region that is determined to be outside the medium. Consequently, itbecomes possible to reduce the number of liquid droplets ejected ontothe region outside the medium, which becomes a necessary evil whenforming dots all the way to the edges of the medium, while substantiallyensuring that the formation of dots at the edges is not impaired.

In the liquid ejection apparatus, the liquid droplets may be ejectedbased on image data formed to a size that is larger than the medium, anda reference region corresponding to the size of the medium may bestored; and the region that is determined to be outside the medium maybe a region that is outside the reference region.

With this liquid ejection apparatus, it is possible to form an image upto the edges of the medium. That is to say, it is possible to form aborderless image.

In the liquid ejection apparatus, the liquid ejection section maycomprise nozzles ejecting the liquid droplets; an image formed on themedium based on the image data may be constituted by raster lines thatare arranged in parallel to one another at a predetermined interval in adirection intersecting the direction of the raster lines, each of theraster lines being made of a multitude of dots arranged on a straightline; and the raster lines may be formed by ejecting the liquid dropletswhile moving the nozzles in the raster line direction.

With this liquid ejection apparatus, an image can be easily formed.

In the liquid ejection apparatus, a ratio at which the liquid dropletsare thinned out in the region that is determined to be outside themedium may be increased toward the edge in the raster line direction.

With this liquid ejection apparatus, less liquid droplets are ejectedwhen approaching the edge of the region in the raster line direction.The reason for this is that the chances that liquid droplets land on themedium become lower toward the edges, so that the influence of thinningthe liquid droplets ejected in the vicinity of the edges is less proneto show up as empty portions in the image. Consequently, it is possibleto reduce the number of liquid droplets while effectively preventing adrop in the image quality due to thinning.

In the liquid ejection apparatus, the nozzles may constitute a nozzlerow in which the nozzles are arranged at a predetermined nozzle pitch ina direction intersecting with the raster line direction; the medium maybe intermittently carried by a predetermined carry amount in theintersecting direction; and in between the intermittent carries, thenozzle row may form the raster lines while moving in the raster linedirection.

With this liquid ejection apparatus, it is possible to form an image onthe medium across a plane that is defined by the raster line directionand a direction intersecting with this direction.

In the liquid ejection apparatus, for a single movement operation of thenozzle row in the raster line direction, the liquid droplets may bethinned out by a predetermined thin-out number consecutively from theedge in the raster line direction and the thin-out number may be thesame number for all of the nozzles constituting the nozzle row; and thethin-out number may be changed for every movement operation of thenozzle row.

With this liquid ejection apparatus, the thin-out number of the liquiddroplets is changed for every movement operation of the nozzle row, sothat the thinned-out state of the liquid droplets at the edge of themedium can be dispersed. Thus, it can be ensured that empty portions inthe image that may become conspicuous at the edges of the medium do notbecome readily apparent.

In the liquid ejection apparatus, the thin-out number of the liquiddroplets may be changed for every movement operation based on apredetermined change pattern, and the thin-out numbers based on thischange pattern may form a cycle that makes a round every time apredetermined number Cm of the movement operations are repeated.

With this liquid ejection apparatus, the thin-out numbers are changedfor each movement operation based on a predetermined change patternwhose unit period is the predetermined number Cm of movement operations.Consequently, it is possible to disperse the thinned-out state of theliquid droplets at the edges, and thus empty portions in the image thatmay become conspicuous at the edges of the medium can be made not to bereadily apparent.

In the liquid ejection apparatus, the nozzle pitch of the nozzle row maybe wider than the interval between the raster lines formed on themedium; and there may be an unformed raster line between raster linesthat are formed by the nozzle row in a single movement operation in theraster line direction.

With this liquid ejection apparatus, it is possible to carry outso-called interlaced printing, which is a print mode in which anunformed raster line is sandwiched between raster lines that are formedby the nozzle row in a single movement operation.

In the liquid ejection apparatus, when the interval between the rasterlines formed on the medium is D, the nozzle pitch is k-D, the number ofthe nozzles ejecting the liquid is N, and the carry amount is F, then: Nmay be coprime with k; and F may be N·D.

With this liquid ejection apparatus, it is possible to reliably performinterlaced printing.

In the liquid ejection apparatus, each of the raster lines formed on themedium may be formed using a plurality of nozzles.

With this liquid ejection apparatus, it is possible to carry outso-called overlap printing, which is a print mode in which the multitudeof dots of a single raster line is formed by a plurality of nozzles.

In the liquid ejection apparatus, the raster line may include anintermittently-ejected portion that is formed by ejecting the liquiddroplets after performing intermittent thinning.

With this liquid ejection apparatus, the raster lines includeintermittently-ejected portions in which the liquid droplets areintermittently thinned out, so that empty portions in the image whichmay become conspicuous at the edges of the medium can be dispersedwithout being continuous in the raster line direction, and can be madenot to be readily apparent.

In the liquid ejection apparatus, a predetermined number Co of movementoperations of the nozzle row may be required to form raster lines at theinterval D on the medium; and the predetermined number Co may be coprimeto the predetermined number Cm regarding the change pattern of thethin-out numbers.

With this liquid ejection apparatus, the predetermined number Co iscoprime to the predetermined number Cm, which is the period of thechange pattern of the thin-out number, thus ensuring that anintermittently-ejected portion is formed.

Moreover, the predetermined number Co, which is the period of themovement operation, is coprime to the predetermined Cm, which is theperiod of the change pattern of the thin-out number, so that thoseperiods can be ensured to be different. Consequently, the periodicity ofthe thinning in the direction of the intermittent carrying can be mademore intricate, and thus empty portions in the image, which may becomeconspicuous at the edges of the medium, can be made less readilyapparent.

In the liquid ejection apparatus, when each raster line is formed by Mnozzles, and when the interval between the raster lines formed on themedium and the interval between the dots in the raster line directionare both D, the nozzle pitch is k·D, the number of the nozzles ejectingthe liquid droplets is N, and the carry amount is F, then: N/M may be aninteger; N/M may be coprime to k; and F may be (N/M)·D.

With this liquid ejection apparatus, overlap printing can be performedreliably.

In the liquid ejection apparatus, k does not have to be a multiple (aninteger multiple other than 1) of the predetermined number Cm.

With this liquid ejection apparatus, k is not a multiple (an integermultiple other than 1) of the predetermined number Cm, so that it can beensured that an intermittently-ejected portion is formed.

In the liquid ejection apparatus, the shape of the dots may besubstantially the shape of an ellipse whose major axis is oriented inthe raster line direction.

With this liquid ejection apparatus, the shape of the dots issubstantially oblong with the major axis oriented in the raster linedirection, so that blanks in the intermittently-ejected portion of theraster lines can be effectively covered, and thus empty portions in theimage can be made less conspicuous.

Further, the liquid ejection apparatus may further comprise an inputsection into which a command is input that indicates whether or not toeject the liquid droplets after thinning; and if a command to eject theliquid droplets after thinning is input, then the liquid droplets may beejected after thinning a suitable number of the liquid droplets that areto be ejected toward the region.

With this liquid ejection apparatus, the user can select whether or notto perform ejection with thinning, thus improving usability.

Furthermore, a liquid ejection apparatus for ejecting a liquid,comprises: a liquid ejection section for ejecting liquid droplets towarda medium in order to form dots on the medium; wherein a mode forejecting the liquid droplets without forming a margin at an edge of themedium can be set; and wherein, if the mode has been set, then: theliquid ejection section ejects, toward a vicinity of the edge of themedium, the liquid droplets of a number that has been thinned out by asuitable number; and at least a portion of the liquid droplets ejectedafter thinning does not land on the medium.

With such a liquid ejection apparatus, an image can be formed up to theedges of the medium. That is to say, it is possible to form a borderlessimage.

Furthermore, a liquid ejection apparatus for ejecting a liquid,comprises: a liquid ejection section for ejecting liquid droplets towarda medium in order to form dots on the medium; and an input section intowhich a command is input that indicates whether or not to eject theliquid droplets after thinning; wherein, if a command to eject theliquid droplets after thinning is input, then when ejecting the liquiddroplets from the liquid ejection section toward a region that isdetermined to be outside the medium, the liquid droplets are ejectedafter thinning a suitable number of the liquid droplets that are to beejected toward that region; wherein the liquid droplets are ejectedbased on image data formed to a size that is larger than the medium, areference region corresponding to the size of the medium is stored, andthe region that is determined to be outside the medium is a region thatis outside the reference region; wherein the liquid ejection sectioncomprises nozzles ejecting the liquid droplets; wherein an image formedon the medium based on the image data is constituted by raster linesthat are arranged in parallel to one another at a predetermined intervalin a direction intersecting the direction of the raster lines, each ofthe raster lines being made of a multitude of dots arranged on astraight line; wherein the raster lines are formed by ejecting theliquid droplets while moving the nozzles in the raster line direction;wherein a ratio at which the liquid droplets are thinned out in theregion that is determined to be outside the medium increases toward theedge in the raster line direction; wherein the nozzles constitute anozzle row in which the nozzles are arranged at a predetermined nozzlepitch in a direction intersecting with the raster line direction;wherein the medium is intermittently carried by a predetermined carryamount in the intersecting direction; wherein, in between theintermittent carries, the nozzle row forms the raster lines while movingin the raster line direction; wherein the nozzle pitch of the nozzle rowis wider than the interval between the raster lines formed on themedium; wherein there is an unformed raster line between raster linesthat are formed by the nozzle row in a single movement operation in theraster line direction; wherein each of the raster lines formed on themedium is formed using a plurality of nozzles; wherein, for a singlemovement operation of the nozzle row in the raster line direction, theliquid droplets are thinned out by a predetermined thin-out numberconsecutively from the edge in the raster line direction and thethin-out number is the same number for all of the nozzles constitutingthe nozzle row; wherein the thin-out number is changed for everymovement operation of the nozzle row; wherein the thin-out number of theliquid droplets is changed for every movement operation based on apredetermined change pattern, and the thin-out numbers based on thischange pattern form a cycle that makes a round every time apredetermined number Cm of the movement operations are repeated; whereina predetermined number Co of movement operations of the nozzle row isrequired to form raster lines at the interval D on the medium; andwherein the predetermined number Co is coprime to the predeterminednumber Cm regarding the change pattern of the thin-out numbers.

With this liquid ejection apparatus, substantially all of theabove-described effects can be attained, so that the object of thepresent invention can be attained most effectively.

It is also possible to achieve a liquid ejection method for ejectingliquid droplets toward a medium in order to form dots on the medium,comprising: a step of thinning out a suitable number of liquid dropletsto be ejected; and a step of ejecting, toward a vicinity of an edge ofthe medium, the liquid droplets of a number that has been thinned out bythe suitable number; wherein at least a portion of the liquid dropletsejected after thinning does not land on the medium.

===Overview of Liquid Ejection Apparatus===

An overview of an inkjet printer serving as an example of a liquidejection apparatus according to the present invention is described inthe following. FIG. 1 to FIG. 4 are diagrams illustrating an overview ofone embodiment of an inkjet printer 1. FIG. 1 shows the externalappearance of this embodiment of the inkjet printer 1. FIG. 2 shows theblock configuration of the inkjet printer 1, and FIG. 3 shows a carriageand a surrounding portion of the inkjet printer 1. FIG. 4 shows thecarrying section of the inkjet printer 1 and its surroundings.

As shown in FIG. 1, the inkjet printer 1 is provided with a structurefor discharging from its front side a print paper S serving as a mediumthat is supplied from its rear side. On its front side, the inkjetprinter 1 is provided with a control panel 2 and a paper dischargesection 3, and on its rear side it is provided with a paper supplysection 4. The control panel 2 is provided with various types of controlbuttons 5 and display lamps 6. The paper discharge section 3 is providedwith a paper discharge tray 7 that blocks the paper discharge openingwhen the inkjet printer is not used. The paper supply section 4 isprovided with a paper supply tray 8 for holding cut paper (not shown).It should be noted that the inkjet printer 1 can also be provided with apaper supply structure with which it is possible to print not onlysingle sheets of the paper S, such as cut paper, but also a continuousmedium such as roll paper.

As shown in FIG. 2, the inkjet printer 1 is provided with a paper carryunit 10, an ink ejection unit 20, a cleaning unit 30, a carriage unit40, a measuring instrument group 50, and a control unit 60, as itsprimary components.

The paper carry unit 10 is for feeding the paper S to a printableposition and moving the paper S in a predetermined direction (thedirection perpendicular to the paper face in FIG. 2 (hereinafter,referred to as the paper carrying direction)) by a predeterminedmovement amount during printing. In other words, the paper carry unit 10functions as a carrying mechanism for carrying the paper S. As shown inFIG. 4, the paper carry unit 10 has a paper insert opening 11A, a rollpaper insert opening 11B, a paper supply motor (not shown), a papersupply roller 13, a platen 14, a paper carry motor (hereinafter,referred to as PF motor) 15, a paper carry motor driver (hereinafter,referred to as PF motor driver) 16, a carry roller 17A, paper dischargerollers 17B, and free rollers 18A and free rollers 18B. However, thepaper carry unit 10 does not necessarily have to include all of thesestructural elements in order to function as a carrying mechanism.

The paper insert opening 11A is where the paper S is inserted. The papersupply motor (not shown) is a motor for carrying the paper S, which hasbeen inserted into the paper insert opening 11A, into the printer 1, andis constituted by a pulse motor. The paper supply roller 13 is a rollerfor automatically carrying the paper S, which has been inserted into thepaper insert opening 11, into the printer 1, and is driven by the papersupply motor 12. The paper supply roller 13 has a transversecross-sectional shape that is substantially the shape of the letter D.The length of the circumference of the paper supply roller 13 is setlonger than the carrying distance to the PF motor 15, so that using thiscircumference the paper S can be carried up to the PF motor 15. Itshould be noted that a plurality of media are kept from being suppliedat one time by the rotational drive force of the paper supply roller 13and the friction resistance of separating pads (not shown).

The platen 14 is a support means that supports the paper S duringprinting. The PF motor 15 is a motor for feeding the paper S in thepaper carrying direction, as shown in FIGS. 2 and 4, and is constitutedby a DC motor. The PF motor driver 16 is for driving the PF motor 15.The carry roller 17A is a roller for feeding the paper S, which has beencarried into the printer by the paper supply roller 13, to a printableregion, and is driven by the PF motor 15. The free rollers 18A (see FIG.4) are provided in a position that is in opposition to the carry roller17A, and push the paper S toward the carry roller 17A by sandwiching thepaper S between them and the carry roller 17A.

The paper discharge rollers 17B (see FIG. 4) are rollers for dischargingthe paper S for which printing has finished out of the printer. Thepaper discharge rollers 17B are driven by the PF motor 15 through a gearwheel that is not shown in the drawings. The free rollers 18B areprovided in a position that is in opposition to the paper dischargerollers 17B, and push the paper S toward the paper discharge rollers 17Bby sandwiching the paper S between them and the paper discharge rollers17B.

The ink ejection unit 20 is for ejecting ink onto the paper S. As shownin FIG. 2, the ink ejection unit 20 has an ejection head 21 serving as aliquid ejection section, and a head driver 22. The ejection head 21 hasa plurality of nozzles, and ejects ink droplets intermittently from thenozzles. The head driver 22 is for driving the ejection head 21, causingink droplets to be ejected intermittently from the ejection head 21.

The cleaning unit 30 is for preventing the nozzles of the ejection head21 from becoming clogged, as shown in FIG. 3. The cleaning unit 30includes a pump device 31 and a capping device 35. The pump device 31 isfor extracting ink from the nozzles in order to prevent the nozzles frombecoming clogged, and includes a pump motor 32 and a pump motor driver33. The pump motor 32 sucks out ink from the nozzles of the ejectionhead 21. The pump motor driver 33 drives the pump motor 32. The cappingdevice 35 is for sealing the nozzles of the ejection head 21 duringstandby, that is, when printing is not being performed, so that thenozzles of the ejection head 21 are kept from becoming clogged.

The carriage unit 40 is for moving the ejection head 21 in apredetermined direction (in FIG. 2, the left-right direction of thepaper face (hereinafter, this is referred to as the ejection headmovement direction)), as shown in FIGS. 2 and 3. It should be noted thatthe ejection head movement direction is perpendicular to the papercarrying direction.

The carriage unit 40 has a carriage 41, a carriage motor (hereinafter,referred to as CR motor) 42, a carriage motor driver (hereinafter,referred to as CR motor driver) 43, a pulley 44, a timing belt 45, and aguide rail 46. The carriage 41 can be moved in the ejection headmovement direction, and the ejection head 21 is fastened to it. Thus,the nozzles of the ejection head 21 intermittently eject ink as they aremoved in the ejection head movement direction. The carriage 41 alsodetachably holds ink cartridges 48 and 49, which contain ink. The CRmotor 42 is a motor for moving the carriage 41 in the ejection headmovement direction, and is constituted by a DC motor. The CR motordriver 43 is for driving the CR motor 42. The pulley 44 is attached tothe rotation shaft of the CR motor 42. The timing belt 45 is driven bythe pulley 44. The guide rail 46 is for guiding the carriage 41 in theejection head movement direction.

The measuring instrument group 50 includes a linear encoder 51, a rotaryencoder 52, a paper detection sensor 53, and a paper width sensor 54.The linear encoder 51 is for detecting the position of the carriage 41.The rotary encoder 52 is for detecting the amount of rotation of thecarry roller 17A. The paper detection sensor 53 is for detecting theposition of the front edge of the paper S to be printed. As shown inFIG. 4, the paper detection sensor 53 is provided in a position where itcan detect the position of the front edge of the paper S as the paper Sis being carried toward the carry roller 17A by the paper supply roller13. It should be noted that the paper detection sensor 53 is amechanical sensor that detects the front edge of the paper S through amechanical mechanism. More specifically, the paper detection sensor 53has a lever that can be rotated in the paper carrying direction, andthis lever is disposed so that it protrudes into the path over which thepaper S is carried. Thus, the front edge of the paper S comes intocontact with the lever and the lever is rotated, and thus the paperdetection sensor 53 detects the position of the front edge of the paperS by detecting the movement of the lever. The paper width sensor 54 isattached to the carriage 41. The paper width sensor 54 is an opticalsensor having a light-emitting section 541 and a light-receiving section543, and detects whether the paper S is in the position of the paperwidth sensor 54 by detecting light that is reflected by the paper S. Thepaper width sensor 54 detects the positions of the edges of the paper Swhile being moved by the carriage 41, so as to detect the width of thepaper S. Depending on the position of the carriage 41, the paper widthsensor 54 can also detect the front edge of the paper S. The paper widthsensor 54 is an optical sensor, and thus detects positions with higherprecision than the paper detection sensor 53.

The control unit 60 is for carrying out control of the printer. As shownin FIG. 2, the control unit 60 includes a CPU 61, a timer 62, aninterface section 63, an ASIC 64, a memory 65, and a DC controller 66.The CPU 61 is for carrying out the overall control of the printer, andsends control commands to the DC controller 66, the PF motor driver 16,the CR motor driver 43, the pump motor driver 32, and the head driver22. The timer 62 periodically generates interrupt signals for the CPU61. The interface section 63 exchanges data with a host computer 67provided outside the printer. The ASIC 64 controls, for example, theprinting resolution and the drive waveforms of the ejection head basedon printing information sent from the host computer 67 through theinterface section 63. The memory 65 is for reserving an area for storingthe programs for the ASIC 64 and the CPU 61 and a working area, forinstance, and includes a storage means such as a RAM or an EEPROM. TheDC controller 66 controls the PF motor driver 16 and the CR motor driver43 based on control commands sent from the CPU 61 and the output fromthe measuring instrument group 50.

In such an inkjet printer 1, when printing, the paper S is carriedintermittently by the carry roller 17A by a predetermined carry amount,and when stopped, that is, between these intermittent carries, inkdroplets are ejected toward the paper S from the ejection head 21 whilethe carriage 41 moves in the direction perpendicular to the carryingdirection of the carry roller 17A, that is, in the ejection headmovement direction. The ink droplets that have been ejected form dots onthe paper S, and a multitude of dots are formed to produce a macroscopicimage on the paper S.

===Ejection Mechanism of the Ejection Head 21===

FIG. 5 is a diagram showing the arrangement of the nozzles for ejectingink droplets that are provided in the lower surface of the ejection head21. As shown in the figure, nozzle rows 211 for the colors black (K),cyan (C), magenta (M), and yellow (Y) are provided in the lower surfaceof the ejection head 21.

Each nozzle row 211 is constituted by a plurality of nozzles #1 to #n.The plurality of nozzles #1 to #n are arranged at a constant interval(nozzle pitch k·D) on a straight line extending in the carryingdirection of the paper S. Here, D is the minimum dot pitch in thecarrying direction (that is, the interval of the dots formed on thepaper S at the highest resolution). Also, k is an integer of 1 orgreater. It should be noted that the nozzles of the nozzle rows areassigned numbers (#1 to #n) that become smaller toward the downstreamside. The nozzle rows 211 are positioned in parallel to one another inthe ejection head movement direction with spaces between them.

It should be noted that in the following description, there are someexplanations given for a single nozzle row of he nozzle rows 211, butthis is because the ejection of ink droplets by the other nozzle rows211 is the same, so that explanations are provided for one row as arepresentative example.

Each of the nozzles #1 to #n is provided with a piezo element (notshown) as a drive element that is used to eject ink droplets. When avoltage of a predetermined duration is applied between electrodesprovided on both ends of the piezo element, the piezo element expands inaccordance with the voltage application time and deforms the lateralwalls of the ink channel. Thus, the volume of the ink channel isconstricted in correspondence with the expansion of the piezo element,causing an amount of ink that corresponds to the amount of theconstriction to be ejected as ink droplets from each of the nozzles #1to #n for each color.

FIG. 6 is a block diagram of a drive circuit for driving the nozzles #1to #n. It should be noted that in FIG. 6 the numbers in parenthesesfollowing each signal name indicate the number of the nozzle to whichthat signal is supplied.

This drive circuit is provided in the head driver 22 shown in FIG. 2 foreach of the four nozzle rows. As shown in FIG. 6, this drive circuit isprovided with an original drive signal generation section 221, aplurality of mask circuits 222, a thinning processing section 224, and adrive signal correction circuit 223.

The original drive signal generation section 221 generates an originaldrive signal ODRV that is used in common by the nozzles #1 to #n. Asshown at the bottom of FIG. 6, the original drive signal ODRV is asignal that includes two pulses, a first pulse W1 and a second pulse W2,during the movement period of a single pixel (during the period that thecarriage 41 moves across the length of a single pixel). The originaldrive signal ODRV that is thus generated is output to each mask circuit222.

The mask circuits 222 are provided in correspondence to the plurality ofpiezo elements that drive the nozzles #1 to #n of the ejection head 21.Each of the mask circuits 222 receives the original signal ODRV from theoriginal signal generation section 221 and also receives print signalsPRT(i), based on the print data PD, which is described below. The printsignals PRT(i) are pixel data corresponding to pixels, and are serialsignals each including the information of two bits for one pixel. Thesetwo bits respectively correspond to the first pulse W1 and the secondpulse W2. The mask circuits 222 a block the original drive signal ODRVor allow it to pass, depending on the level of the print signal PRT(i).That is to say, when the print signal PRT(i) is at level 0, the pulse ofthe original drive signal ODRV is blocked and no ink droplet is ejected,whereas when the print signal PRT(i) is at level 1, the correspondingpulse of the original drive signal ODRV is passed unchanged, so that itis output via the driving signal correction section 223 to the piezoelement as a drive signal DRV(i), and thus an ink droplet is ejectedfrom the nozzle.

It should be noted that in this embodiment, a thinning signal SIG isinput from the thinning processing section 224 into the mask circuits224, in addition to the print signal PRT(i). This thinning signal SIG isused for a thinning process when performing borderless printing asdescribed below, and is a signal that is either at level 0 or level 1.Whether the drive signal DRV(i) that has passed the mask circuit 224becomes a signal that causes ejection of an ink droplet is determined bythe calculation of the logical product (so-called “AND” operation) ofthe print signal PNT(i) and the thinning signal SIG.

As shown in FIG. 6, in the present embodiment, the same thinning signalSIG is input into all nozzles of a nozzle row 211. Consequently, theposition in the ejection head movement direction when no ink droplet isto be ejected based on this thinning signal SIG is the same for allnozzles. This is related to the Rule 1 of the later-described thinningprocess.

The thinning signal SIG is generated for each pixel in the ejection headmovement direction, in order to perform the later-described thinningprocess, and is input into the mask circuits 222 in correspondence withthe print signals PRT(i). It should be noted that this thinning processis described further below.

The drive signal correction section 223 carries out a correction byshifting the timing of the drive signal waveforms shaped by the maskcircuits 222 forward or backward for the entire return pass. Bycorrecting the timing of the drive signal waveforms, misalignments inthe locations where the ink droplets land in the forward pass and in thereturn pass are corrected. That is, the misalignment in the positionswhere dots are formed in the forward pass and the return pass iscorrected.

===Processing in the Host===

FIG. 7 is a diagram for schematically describing the processing in thehost 67. As shown in the diagram, the host 67 is provided with a maincomputer unit 90, which is connected to the printer 1, and a displaydevice 93. A computer program 96 known as a “printer driver” forcontrolling operation of the printer 1 is installed in the computer 90.As shown in the diagram, the printer driver 96 operates under apredetermined operating system that is installed on the host 67 andunder which an application program 95 also operates. The operatingsystem includes a video driver 91 and a printer driver 96, and theapplication program 95 outputs print data PD for transfer to the inkjetprinter 1 through these drivers. The application program 95, whichcarries out retouching of images, for example, performs desiredprocessing with respect to an image to be processed, and also displaysthe image on the display device 93 via the video driver 91.

When the application program 95 issues a print command, the printerdriver 96 of the main computer unit 90 receives image data from theapplication program 95 and converts the image data into print data PD tobe supplied to the inkjet printer 1. The printer driver 96 is internallyprovided with a resolution conversion module 97, a color conversionmodule 98, a halftone module 99, a rasterizer 100, a user interfacedisplay module 101, a UI printer interface module 102, and a colorconversion lookup table LUT.

The resolution conversion module 97 performs the function of convertingthe resolution of color image data formed by the application program 95to the print resolution. The image data that is thus converted inresolution is still image information composed of the three colorcomponents RGB. The color conversion module 98 references the colorconversion lookup table LUT as it converts the RGB image data for eachpixel into multi-gradation data of a plurality of ink colors that can beused by the printer 1. The color-converted multi-gradation data has 256gradation values, for example. The halftone module 99 carries out aso-called halftoning process, generating halftone image data. Thehalftone image data is rearranged by the rasterizer 100 into the dataorder in which it is to be transferred to the printer 1, and is outputas the final print data PD to the printer 1. The print data PD includesraster data that indicates how dots are formed when the ejection headmoves, and data indicating the carry amount of the paper S.

The user interface display module 101 has a function for displayingvarious types of user interface windows related to printing and afunction for receiving user inputs through those windows.

The UI printer interface module 102 functions as an interface betweenthe user interface (UI) and the printer 1. It interprets instructionsgiven by users through the user interface and sends various commands COMto the printer 1, or conversely, it also interprets commands COMreceived from the printer 1 and performs various displays on the userinterface.

It should be noted that the printer driver 96 executes, for example, afunction for sending and receiving various types of commands COM and afunction for supplying print data PD to the printer 1. A program forexecuting the functions of the printer driver 96 is supplied in a formatin which it is stored on a computer-readable storage medium. Examples ofthis storage medium include various types of media from which the host67 can read data, such as flexible disks, CD-ROMs, magneto opticaldisks, IC cards, ROM cartridges, punch cards, printed materials on whicha code such as a bar code is printed, internal storage devices (memoriessuch as a RAM or a ROM) and external storages devices of the host 67.The computer program can also be downloaded onto the main computer unit90 via the Internet.

===Print Modes===

Here, print modes that can be executed by the printer 1 of the presentembodiment are described using FIGS. 8A, 8B, 9A and 9B. Two print modes,namely interlaced printing and overlap printing can be executed. Byusing these print modes as appropriate, individual differences betweenthe nozzles, such as in the nozzle pitch and the ink ejectionproperties, are lessened by spreading them out over the image to beprinted, and thus an improvement in image quality can be attained.

<Regarding Interlaced Printing>

FIGS. 8A and 8B are explanatory diagrams of ordinary interlacedprinting. It should be noted that for the sake of simplifying thedescription, a nozzle row, which is shown in place of the ejection head21, is illustrated to be moving with respect to the paper S, but thediagrams show the relative positional relationship between the nozzlerow and the paper S, and in fact it is the paper S that moves in thecarrying direction. In the diagrams, the nozzles represented by blackcircles are the nozzles that actually eject ink droplets, and thenozzles represented by white circles are nozzles that do not eject inkdroplets. FIG. 8A shows the nozzle positions in the first through fourthpasses and how the dots are formed by those nozzles. FIG. 8B shows thenozzle positions in the first through sixth passes and how the dots areformed.

Here, “interlaced printing” refers to a print mode in which k is atleast 2 and a raster line that is not recorded is sandwiched between theraster lines that are recorded in a single pass. Also, “pass” refers toa single movement of the nozzle row in the ejection head movementdirection. “Rasterline” refers to a row of pixels lined up in theejection head movement direction. “Pixels” are the square boxes that aredetermined virtually on the print paper S in order to define thepositions where ink droplets are caused to land so as to record dots.

Throughout this specification, to simplify explanations, the pixels aretreated as being virtually present not only on the paper S, but also inthe abandonment region Aa, which extends beyond the outer edges of thepaper S, as shown in FIGS. 15A and 15B. Consequently, as shown in thesefigures, the “edge of the raster lines” mentioned below does not meanthe edge of the paper S, but it means the lateral edge of theabandonment region Aa.

With the interlaced printing illustrated in FIG. 8A and FIG. 8B, eachtime the paper S is carried in the carrying direction by a constantcarry amount F, each nozzle records a raster line immediately above theraster line that was recorded in the pass immediately before. In orderto record the raster lines in this way using a constant carry amount,the number N (which is an integer) of nozzles that actually eject ink isset to be coprime to k, and the carry amount F is set to N·D.

In the figures, the nozzle row has four nozzles arranged in the carryingdirection. However, since the nozzle pitch k of the nozzle row is 4, notall the nozzles can be used so that the condition for interlacedprinting, that is, “N and k are coprime”, is satisfied. Therefore, threeof the four nozzles are used to perform interlaced printing.Furthermore, because three nozzles are used, the paper S is carried by acarry amount 3·D. As a result, for example a nozzle row with a nozzlepitch of 180 dpi (4·D) is used to form dots on the paper S at a dotpitch of 720 dpi (=D).

The figures show the manner in which consecutive raster lines areformed, with the first raster line being formed by the nozzle #1 of thethird pass, the second raster line being formed by the nozzle #2 of thesecond pass, the third raster line being formed by the nozzle #3 of thethe fourth pass. It should be noted that ink droplets are ejected onlyfrom the nozzle #3 in the first pass, and ink droplets are ejected onlyfrom the nozzle #2 and the nozzle #3 in the second pass. The reason forthis is that if ink droplets were ejected from all of the nozzles in thefirst and second passes, it would not be possible to form consecutiveraster lines on the paper S. From the third pass on, the three nozzles(#1 to #3) eject ink droplets and the paper S is carried by a constantcarry amount F (=3-D), forming consecutive raster lines at the dot pitchD.

<Regarding Overlap Printing>

FIGS. 9A and 9B are explanatory diagrams of ordinary overlap printing.With the above-described interlaced printing, a single raster line isformed by a single nozzle, whereas with overlap printing, a singleraster line is formed, for example, by two or more nozzles.

That is, with overlap printing, each time the paper S is carried by aconstant carry amount F in the carrying direction, the nozzles, whichmove in the raster line direction, intermittently eject ink dropletsevery several dots, thereby intermittently forming dots in the rasterline direction, which is the ejection head movement direction. Then, inanother pass, dots are formed such that the intermittent dots alreadyformed by other nozzles are completed in a complementary manner. Thus, asingle raster line is completed by a plurality of nozzles. The number ofpasses M needed to complete a single raster line is defined as the“overlap number M”. In the figure, since each nozzle forms dotsintermittently at every other dot, dots are formed in every pass eitherat the odd-numbered pixels or at the even-numbered pixels. Since asingle raster line is formed using two nozzles, the overlap number isM=2. It should be noted that the overlap number is M=1 in the case ofinterlaced printing described above.

In overlap printing, the following conditions are necessary in order tocarry out recording with a constant carry amount: (1) N/M is an integer,(2) N/M and k are coprime, and (3) the carry amount F is set to (N/M)·D.

In the figures, the nozzle row has eight nozzles arranged in thecarrying direction. However, since the nozzle pitch k of the nozzle rowis 4, in order to fulfill the condition for performing overlap printing,which is that “N/M and k are coprime,” not all the nozzles can be used.Therefore, six of the eight nozzles are used to perform overlapprinting. Furthermore, because six nozzles are used, the paper S iscarried by a carry amount 3·D. As a result, for example a nozzle rowwith a nozzle pitch of 180 dpi (4·D) is used to form dots on the paper Sat a dot pitch of 720 dpi (=D). Furthermore, in a single pass, eachnozzle forms dots intermittently in the ejection head movement directionat every other dot. In the figure, the raster lines in which two dotsare written in the ejection head movement direction are alreadycompleted. For example, in FIG. 9A, the first through the sixth rasterlines have already been completed. On the other hand, raster lines inwhich only one dot is written are raster lines in which dots have beenformed intermittently at every other dot. For example, in the seventhand tenth raster lines, dots are formed intermittently at every otherdot. It should be noted that the seventh raster line, in which dots havebeen intermittently formed at every other dot, is completed by havingthe nozzle #1 fill it up in the ninth pass.

The figures show the manner in which consecutive raster lines areformed, with the first raster line being formed by the nozzle #4 in thethird pass and the nozzle #1 in the seventh pass, the second raster linebeing formed by the nozzle #5 in the second pass and the nozzle #2 inthe sixth pass, the third raster line being formed by the nozzle #6 inthe first pass and the nozzle #3 in the fifth pass, and the fourthraster line being formed by the nozzle #4 in the fourth pass and thenozzle #1 in the eighth pass. It should be noted that in the first tosixth passes, some of the nozzles #1 to #6 do not eject ink. The reasonfor this is that if ink were ejected from all of the nozzles in thefirst to sixth pass, it would not be possible to form consecutive rasterlines on the paper S. From the seventh pass on, the six nozzles (#1 to#6) eject ink and the paper S is carried by a constant carry amount F(=3·D), forming consecutive raster lines at the dot pitch D. TABLE 1sec- sev- first ond third fourth fifth sixth enth eighth pass pass passpass pass pass pass pass pass recorded odd even odd even even odd evenodd pixel

Table 1 describes the positions in the ejection head movement directionwhere dots are formed in each pass. In the table, “odd” means that dotsare formed at odd-numbered pixels of the pixels lined up in the ejectionhead movement direction (pixels in a raster line). Moreover, “even” inthe table means that dots are formed at even-numbered pixels of thepixels lined up in the ejection head movement direction. For example, inthe third pass, the nozzles form dots at odd-numbered pixels. When asingle raster line is formed by M nozzles, k×M passes are required inorder to complete a number of raster lines corresponding to the nozzlepitch. For example, in this embodiment, a single raster line is formedby two nozzles, so that 8 (4×2) passes are required in order to completefour raster lines. As can be seen from Table 1, in the four passesduring the first half, dots are formed in the order ofodd-even-odd-even. Consequently, when the four passes during the firsthalf have been finished, dots are formed at even-numbered pixels inraster lines adjacent to raster lines in which dots are formed atodd-numbered pixels. In the four passes during the second half, dots areformed in the order of even-odd-even-odd. In other words, in the fourpasses during the second half, dots are formed in reverse order withrespect to the four passes during the first half. Consequently, dots areformed so as to fill up gaps between the dots that have been formed inthe passes during the first half.

===Borderless Printing===

“Borderless printing” is described below. “Borderless printing” is amethod of printing in which no margins are formed at the edge portionsof the print paper S. In the inkjet printer 1 according to thisembodiment, by selecting the print mode it is possible to execute either“borderless printing” or “regular printing.”

In “regular printing,” printing is performed in such a manner that theprint region A, which is the region onto which ink droplets are ejected,fits on the print paper S. FIG. 10 shows the relationship between thesizes of the print region A and the paper S during “regular printing.”The print region A is set such that it fits on the paper S, and marginsare formed at the upper and lower edges as well as at the left and rightedges of the paper S.

When “regular print mode” is set as the print mode in order to perform“regular printing,” the printer driver 96 generates print data PD sothat the print region A fits on the paper S based on image data receivedfrom the application program. For example, when processing image data inwhich the print region A does not fit within the paper S, a portion ofthe image that is expressed by the image data is disregarded whenprinting or the image is shrunken, for example, so that the print regionA fits on the paper S.

FIG. 11 shows the relationship between the sizes of the print region Aand the paper S during “borderless printing.” The print region A is alsoset with respect to a region that extends beyond the top and bottomedges and the left and right edges of the paper S (hereinafter, referredto as the abandonment region Aa), and ink droplets are ejected onto thisregion as well. Thus, even when the position of the paper S is somewhatshifted with respect to the ejection head 21 as a result of thepositioning accuracy when the paper is carried, for example, inkdroplets can be reliably ejected toward the edge portions of the paper Sto form dots thereon, thereby preventing margins from being formed atthe edge portions. It should be noted that “borderless printing” doesnot always have to be performed with respect to all of the top andbottom edge portions and the left and right edge portions of the paper Sas shown in FIG. 11, and sometimes it may also be performed for only oneof these edge portions.

When the “borderless print mode” has been set as the print mode in orderto perform “borderless printing,” the printer driver 96 generates printdata PD in which the print region A extends beyond the paper S by apredetermined width, based on the image data. For example, whenprocessing image data in which the print region A is smaller than thepaper S, the image is enlarged so that the print region A covers theentire paper S and extends beyond the paper S by the predeterminedamount. Conversely, when processing image data in which the print regionA extends significantly beyond the paper S, the image is shrunken sothat the amount by which the print region extends beyond the paper Sbecomes the predetermined width. It should be noted that when performingscaling adjustment through enlarging or shrinking in order to ensure thepredetermined width, if the aspect ratio of the image is changed fromthat of the original image and the image is distorted, a portion of theimage may be eliminated from the printing target after the scalingadjustment so that the predetermined width is secured while maintainingthe aspect ratio of the original image.

Describing this adjustment by scaling in more detail, the printer driver96 stores a region having the same size as the standard size of thepaper S in the memory 65 as a reference region As. The printer driver 96references the reference region As to generate print data PD byexpanding the image data to a size where it extends outside thereference region As by the predetermined width in the ejection headmovement direction and the carrying direction. The portion correspondingto this predetermined width is the region that is determined to beoutside of the paper S, and is the abandonment region Aa in which inkdroplets are abandoned.

The reference region As and the predetermined width are stored in thememory 65 for each paper size, such as postcard size and A4 size, andare read individually based on the paper size information that is inputby the user and then used for the above-described scaling adjustment.

Incidentally, if paper carrying is performed correctly and the paper Sis precisely positioned in a predetermined design position, then thereference region As will match the paper S and the image in thereference region As will be printed on the paper S. However, if there isa positional shift, then the image of the abandonment region Aa will beprinted onto the edge portions of the paper S.

<Processing the Abandoned Ink>

In “borderless printing,” abandoned ink droplets that land outside thepaper S can have negative effects, such as adhering to the platen 14 andmaking it dirty. For this reason, the platen 14 of the printer 1according to this embodiment is provided with an ink collection section80 for collecting ink droplets that have missed the paper S.

FIG. 12 is a plan view of the ink collection section 80. The inkcollection section 80 is broadly divided into two sections, these beinga first ink collection section 82 shown in the cross-sectional views ofFIGS. 13A and 13B and a second ink collection section 83 shown in thecross-sectional view of FIG. 14. The first ink collection section 82 isused when performing borderless printing with respect to the top andbottom edge portions of the paper S, and the second ink collectionsection 83 is used when performing borderless printing with respect tothe left and right edges of the paper S.

As shown in FIGS. 12 to 14, both of the first and second ink collectionsections 82 and 83 are formed in the platen 14 as grooves having adepressed cross-sectional shape. An absorbing member 84 such as a spongefor absorbing ink droplets is arranged in the grove portions. Theabandoned ink droplets reach the top of the absorbing member 84 and areabsorbed by the absorbing member 84.

The groove portion of the first ink collection section 82 shown in FIGS.12, 13A and 13B is arranged in a straight line along the movementdirection of the carriage 41 (ejection head movement direction), and theposition of the groove in the carrying direction is in opposition tosubstantially the middle of the ejection head 21, that is, it is inopposition to nozzles #k to #k+4. Consequently, when borderless printingis performed with respect to the top edge portion as shown in FIG. 13A,ink droplets are ejected only from the nozzles #k to #k+4 prior to thetop edge of the paper S arriving at the first ink collection section 82.On the other hand, when borderless printing is performed with respect tothe bottom edge portion, then as shown in FIG. 13B, ink droplets areejected only from the nozzles #k to #k+4 after the bottom edge portionof the paper S has passed over the first ink collection section 82.Then, while printing these top and bottom edge portions, ink dropletsejected from the nozzles #k to #k+4 that have not landed on the paper Sland on the absorbing member 84 in the first ink collection section 82,and thus the upper surface of the platen 14 will not become dirty due tothese abandoned ink droplets.

The groove portions of the second ink collection section 83 shown inFIGS. 12 and 14 are provided at positions where they are in oppositionto the left and right edge portions of the paper S, and both of thesegroove portions are formed in straight lines in the carrying directionof the paper S. When borderless printing is performed with respect tothe left and right edge portions, ink droplets are ejected from nozzlesduring movement of the carriage 41 not only when the carriage 41 ismoving over the print paper S but also when it is moving over theabandonment region Aa outside the lateral edge portions of the paper S.Here, ink droplets ejected onto the abandonment region Aa land on theabsorbing member 84 in the second ink collection sections 83, so thatthe platen 14 will not become dirty due to these abandoned ink droplets.

===Regarding the Process of Thinning Out Ink Droplets During BorderlessPrinting===

As mentioned above, it is necessary to set the aforementionedabandonment region Aa in order to perform “borderless printing”, butmost of the ink droplets ejected toward this abandonment region Aa donot contribute to the formation of the image and are wasted, so that itis desirable to make the number of ink droplets ejected toward theabandonment region as small as possible. Also, these abandoned inkdroplets are ejected with the goal of not forming a margin at the edgesof the paper S, and considering this aspect, it seems to be sufficientif the number of ink droplets is decreased by thinning the number of inkdroplets to an extent that no empty portions that can be perceived as amargin at the edges are formed in the image, that is, to an extent thatdoes not become conspicuous.

Consequently, in accordance with the present invention, ejection isperformed after a suitable number of ink droplets is thinned out fromthe ink droplets to be ejected toward the abandonment region Aa, thatis, the region that is determined to be outside the paper S, to anextent that does not become readily apparent.

FIGS. 15A and 15B are plan views schematically showing the thinned stateat this abandonment region Aa, and show the print region A based on theprint data PD overlaid over the reference region As that corresponds tothe paper S. It should be noted that in these figures, pixels onto whichink droplets are ejected are marked as black circles, whereas thinnedout pixels onto which no ink droplets are ejected are marked as whitecircles. Also, for the sake of explanation, the uppermost raster line inthe figures is referred to as the first raster line R1. Thereafter, indownward direction, the raster lines are successively referred to as thesecond raster line R2, the third raster line R3, etc.

In the example shown in FIG. 15A, the ink droplets ejected onto theabandonment region are thinned out at every other line of the rasterlines R1, R2, etc. lined up in the carrying direction. That is to say,ink droplets are not ejected onto the abandonment region Aa at rasterlines (for example R2 and R4) that sandwich, with respect to thecarrying direction, a raster line in which ink droplets are ejected ontothe abandonment region Aa (for example R3).

In the example shown in FIG. 15B, there is no thinning in the firstraster line R1. In the second raster line R2 below that, one pixel eachis thinned out from both edges, and in the third raster line R3 furtherbelow, two pixels each are thinned out from both edges. This pattern isrepeated in that order in the following raster lines R4, R5 . . . . Aplurality of thinning regions of triangular shape when viewed from aboveare formed along the carrying direction in the thusly thinned outabandonment region Aa.

It should be noted that in both of these two examples, the ratio ofthinned out ink droplets with respect to a unit surface area of theabandonment region Aa is the same. That is to say, one out of every twopixels is thinned out. However, if ink droplets are thinned out at thesame ratio, then it is preferable that the ratio by which ink dropletsare thinned out is increased toward the edges in the raster linedirection, as shown in FIG. 15B. Describing this in more detail, whenthe abandonment regions Aa shown in FIG. 15A and FIG. 15B are viewedalong the carrying direction, there are two pixels rows L1 and L2extending along the carrying direction formed in the abandonment regionAa. In the example of FIG. 15A, one out of every two pixels is thinnedout in both the pixel row L1 on the inner side and in the pixel row L2outward of this pixel row L1. On the other hand, in the example of FIG.15B, one out of every three pixels is thinned out in the pixel row L1 onthe inner side, whereas two out of every three pixels are thinned out inthe pixel row L2 on the outer side. Thus, in this FIG. 15B, the ratio bywhich ink droplets are thinned out increases toward the edge in theraster line direction.

The reason why the example in FIG. 15B is preferable is because, thefarther the position is from the reference region As, which correspondsto the size of the paper S, the lower the possibility that the positionof the paper S will shift to such a far position, and the lower thepossibility that the effect of thinning the ink droplets will becomevisible as empty portions in the image on the paper S.

The selection of whether this thinning process is carried out or not canbe made for example with the user interface display module 101. That isto say, a button for instructing execution and a button for instructingnon-execution of the thinning process are selectably displayed in awindow for the printer driver of the user interface display module 101,and the user can choose whether or not to carry out the thinning processwith these buttons.

It should be noted that a signal for the selected button is output tothe printer 1, in association with the print data PD that is generatedby the printer driver. Then, as shown in the flowchart in FIG. 15C, ifthe signal of the non-execution button has been associated, the thinningprocessing section 224 of FIG. 6 in the head driver 22 does nothing,whereas if the signal of the execution button has been associated, thethinning processing section 224 generates a thinning signal SIG so as toachieve the above-described thinned-out state, and sends this thinningsignal SIG to the mask circuits 222 in correspondence with the printsignals PRT(i) entered into the mask circuits 222 (see Steps S10 andS20). That is to say, the thinning signal SIG is given into the maskcircuits 222 in addition to the print signals PRT(i), and whether inkdroplets are ejected toward the pixels corresponding to the printsignals PRT(i) is determined by the logical product (so-called AND) ofthe print signal PRT(i) and the thinning signal SIG. The thinning signalSIG is set for each pixel of the abandonment region Aa, and it is set tolevel 0 for the pixels in this region Aa onto which no ink droplets areejected, whereas it is set to level 1 for the pixels onto which inkdroplets are ejected.

Incidentally, to simplify explanations, it is assumed that the printdata PD in the examples of FIG. 15A and FIG. 15B is data for a solidimage in which ink droplets are ejected over the entire surface of theprint region Aa, that is, the print signals PRT(i) of the entire printdata PD are at level 1. On the other hand, in the actual print data PD,there may be pixels in which the print signal PRT(i) is at level 0;therefore, the actual thinned-out state that is apparent on anactually-printed paper S is a cross of the two, that is, also pixelsmarked by black circles in the abandonment region Aa may become whitecircles, depending on the print signal PRT(i). It should be noted thatalso in the following explanations, it is assumed that the print data PDis data for recording solid images.

===Examples of the Thinning Process===

As an example of the thinning process, an example is explained in whichborderless printing is performed at the right edge of the paper S. Asfor the print mode, explanations are given for interlaced printing andfor overlap printing, respectively.

FIGS. 16 to 31 are diagrams showing by which nozzle and in which passthe raster lines in the vicinity of the right edge of the print paper Sare formed. The portion on the left side (referred to as left diagram inthe following) in the figures indicates the relative position of thenozzle row with respect to the paper S in each pass. It should be notedthat in the left diagrams, for illustrative reasons, the nozzle row isshown moving downward in increments of the carry amount F for each pass,but in actuality the paper S is moved in the carrying direction. Thenozzle numbers in the nozzle row are shown as circled numbers.

To the right of the left diagram it is shown how ink droplets areejected toward the reference region As and the abandonment region Aa(referred to as right diagram in the following). The square boxes in theright diagram each represent one pixel, and the numbers written intothese boxes indicate the number of the nozzle ejecting ink dropletstoward that pixel. Also, pixels into which no nozzle number is writtenare pixels onto which no ink droplet is ejected, that is, pixels thatare thinned out by the thinning process. It should be noted that thethin-out numbers shown below the left diagram indicate the number ofpixels that are thinned out from the abandonment region Aa in each pass.

On the right-hand side of the right diagram, there is the lateral edgeof the reference region As, and even further to the right, anabandonment region Aa whose width in the ejection head movementdirection is eight pixels (FIGS. 16 through 23) or 32 pixels (FIGS. 24through 31) is set, and the edges of the raster lines are located at theouter border of the abandonment region Aa.

For the sake of explanation, the uppermost raster line in the figures isreferred to as the first raster line R1. Thereafter, in downwarddirection, the raster lines are successively referred to as the secondraster line R2, the third raster line R3, and so forth. Also, the rightdiagram selectively shows only a portion with respect to the carryingdirection, but needless to say, raster lines are formed consecutivelyalso above the uppermost first raster line R1 and below the lowermosttwenty-fifth raster line R25 in the figure.

The thinning processing section 224 according to the present embodimentforms the thinning signal SIG in accordance with the following fourrules, and inputs the thinning signal SIG into the mask circuits 222 incorrespondence with the print signals PRT(i), thus thinning the numberof ink droplets in the abandonment region Aa.

Rule 1:

The thin-out number, which is the number of pixels onto which no inkdroplets are ejected, is set for every single pass (for every movementof the ejection head). This thin-out number is set as a common value forall nozzles, and in that pass, the positions of the thinned out pixelsin the ejection head movement direction are the same for all nozzles.

This Rule 1 is explained with the example of interlaced printing shownin FIG. 16. In the fourth pass shown in the left diagram, the fourth,the eighth and the twelfth raster lines R4, R8 and R12 are respectivelyformed by the nozzles #1, #2 and #3, and in this fourth pass, thethin-out number is set to 2, as shown below the left diagram.Consequently, none of the three nozzles #1, #2 and #3 eject ink dropletsonto two of the pixels in the raster lines that they form. Moreover, theposition of those pixels in the ejection head movement direction is thesame for all three nozzles #1, #2 and #3, and in the example shown inthe figure, the first and the second pixel from the edge are thinned outfrom the raster lines R4, R8 and R12.

Rule 2:

The positions of the thinned out pixels in the ejection head movementdirection in each pass are selected from the positions onto which inkdroplets can be ejected in that single pass, and the pixels at thepositions that are candidates for selection are set by counting up tothe thin-out number from the edges of the raster lines.

Explaining this Rule 2 in more detail with reference to FIGS. 16 and 25,in the case of interlaced printing shown in FIG. 16, ink droplets can beejected onto all pixels lined up in the raster line direction in asingle pass. Consequently, the positions of the thinned out pixels inthe ejection head movement direction in the fourth pass in the leftdiagram are designated by counting the pixels up to the thin-out number2 for the fourth pass from the edge of each of the raster lines R4, R8and R12 as shown in the right diagram, thus designating two consecutivepixels from the edge.

On the other hand, in the case of overlap printing as shown in FIG. 25,ink droplets can be ejected only intermittently in a single pass atevery M−1 pixels onto the pixels lined up in the raster line direction.For example, if the overlap number M is 2, then ink droplets can beejected only onto odd-numbered pixels in the raster line direction in agiven single pass, whereas the ink droplets for the even-numbered pixelsbetween these odd-numbered pixels can only be ejected in another singlepass. Consequently, in the case of overlap printing, the thinned outpixels in each pass are designated by counting every (M−1)-th one of thepixels making up the raster line up to the thin-out number from theedge. This is explained in further detail with reference to the examplein FIG. 25. In the third pass in this example, ink droplets can beejected onto the odd-numbered pixels of the first, fifth and ninthraster lines R1, R5 and R9, and the thin-out number of this third passis set to 16, as shown below the left diagram. Consequently, thedesignation is performed by counting 16 of the odd-numbered pixels fromthe edge of each of the raster lines R1, R5 and R9, and no ink dropletsare ejected onto these designated 16 pixels. It should be noted thatsince the 16 pixels are designated for every other pixel, the result isthat pixels located up to the 32^(rd) pixel from the edge of the rasterlines are designated.

Rule 3:

The thin-out number changes for each pass, in accordance with apredetermined change pattern. The pass number Cm through which thethin-out numbers cycle in accordance with the change pattern is referredto as the change period Cm of the thin-out numbers.

This Rule 3 is explained in more detail with reference to FIG. 16. Belowthe left diagram, the thin-out number corresponding to each pass isshown. In the example of this figure, the change pattern is such apattern that repeats the thin-out numbers 0 and 2 in each pass, and thechange period Cm, which is the number of passes through which thischange pattern cycles, is 2 passes. That is to say, in this example, thethin-out number of the first pass is 0, and the thin-out number of thesecond pass is 2, and in the following passes, this is repeated in thisorder.

Rule 4:

The change pattern of the thin-out number is as follows. Here, j is aninteger of 1 or greater. TABLE 2 first second third fourth fifth sixthseventh eighth ninth pass pass pass pass pass pass pass pass pass passthin-out 0 j 4j 2j 0 3j 2j 4j 0 number (pixels)

j is an integer of 1 or greater.

It should be noted that if a number smaller than nine passes is set asthe change period Cm, then the thin-out number of the passes until thatset number is repeated. For example, if the change period Cm is set to 3passes, then 0, j and 4j (where j is an integer of 1 or greater), whichare the thin-out numbers of the first to third passes in Table 2, arerepeated in that order. Incidentally, the change pattern shown in Table2 is the pattern that is most preferable with regard to scattering thethinned-out state, and has been found through the “discussion ofpreferable change patterns” further below.

<Example of the Thinning Process for Interlaced Printing>

FIGS. 16 through 23 show an example of the thinning process for the caseof interlaced printing. In FIGS. 16 to 23, the change period Cm of thethin-out numbers is different in each drawing, thus illustrating theinfluence of the change period Cm on the thinned-out state. However, theconditions for interlaced printing are the same in all figures. That isto say, the nozzle number N ejecting ink droplets is N=3, the nozzlepitch is k·D=4·D, and the carry amount is F(=N·D)=3·D.

First, the raster line formation process with interlaced printing isexplained with reference to FIG. 16. It should be noted that sinceinterlaced printing has been explained before, only the aspects that arenecessary for the understanding of the present example are explainedhere.

As shown in FIG. 16, in the third pass, the first raster line R1 isformed by the nozzle #1, the fifth raster line R5 is formed by thenozzle #2, and the ninth raster line R9 is formed by the nozzle #3. Thesecond, third and fourth raster lines R2, R3 and R4 that lie between thefirst raster line R1 and the fifth raster line R5 are formed by thenozzle #2 in the second pass, the nozzle #3 in the first pass and thenozzle #1 in the fourth pass, respectively. This means that in order toconsecutively form the first to fifth raster lines, a total of fourpasses from the first pass to the fourth pass are necessary. In otherwords, in the interlaced printing according to the present example, fourpasses form one cycle, and raster lines are formed consecutively at adot pitch D in the carrying direction by repeating this cycle. In thefollowing, this one cycle is referred to as “interlacing cycle.” In thefigures, the first interlacing cycle, which is made of four passes, istaken to be the i-th cycle, and the interlacing cycle made of the nextfour passes is taken to be the (i+1)-th cycle.

The following is an explanation of the thinning process in theabandonment region Aa.

As shown in FIG. 16, an abandonment region Aa with a width of eightpixels in the ejection head movement direction is set to the right ofthe reference region As, and the edges of the raster lines are locatedat the outer border of this abandonment region Aa. Moreover, in eachpass, a thinning process based on the thin-out number corresponding tothat pass is performed, so that when forming the raster lines of eachpass, a number of pixels corresponding to the thin-out number is countedfrom the edge of each raster line and designated, and no ink dropletsare ejected onto the designated pixels. It should be noted that tofacilitate the drawings, the number of pixels in the ejection headmovement direction constituting the abandonment region Aa has been setto eight, but there is no limitation to this.

As shown below the left diagram in FIGS. 16 to 23, the change period Cmof the thin-out number is changed from two to nine passes from FIG. 16to FIG. 23, respectively. The change pattern of the thin-out number forthese examples is obtained by setting the value j in Table 2 to “2”. Forexample, in the case of FIG. 16 where the change period Cm is 2 passes,the thin-out number for each pass repeats the cycle of 0 and 2. Further,in the case of FIG. 16 where the change period Cm is 3 passes, thethin-out number repeats the cycle of 0, 2, and 8. As for the four tonine passes in FIGS. 18 to 23, every time the change period Cm increasesby one, one of the numbers 4, 0, 6, 4, 8 and 0 is added in this order asthe thin-out number of the corresponding fourth and further passes.

This is explained taking FIG. 17, in which the change period Cm is 3passes, as a representative example of all figures. As shown below theleft diagram, the thin-out number changes at each pass in the order of0-2-8. This change pattern is repeated for all passes of the interlacedprinting.

For example, the thin-out number of the first pass of the i-th cycle is0, so that there is no thinning in the third raster line R3 formed inthis first pass, and the ink droplets are ejected by the nozzle #3 ontothe eight pixels up to the edge of the raster line. In the followingsecond pass, the thin-out number is 2, so that two pixels from the edgeof the raster lines are thinned out from the second raster line R2 andthe sixth raster line R6 formed in this second pass, and ink dropletsare ejected from the nozzles #2 and #3 onto the remaining six pixels. Inthe following third pass, the thin-out number is 8, so that eight pixelsfrom the edge of the raster lines are thinned out from the first, fifthand ninth raster lines R1, R5 and R9 formed in this third pass, that is,no ink droplets are ejected from the nozzles #1, #2 and #3 onto theabandonment region Aa. Furthermore, in the following fourth pass, thechange pattern completes the cycle and returns to a thin-out number of0, so that the fourth, eighth and twelfth raster lines R4, R8 and R12formed in this fourth pass are formed without thinning, as in the firstpass, that is, ink droplets are ejected onto the eight pixels up to theedge of the raster lines.

Here, when looking at the abandonment regions Aa from FIG. 16 to FIG. 23macroscopically, the thinning ratio becomes larger when approaching theedges of the raster lines. This is because the thinned out pixels aredesignated by counting the thin-out number from the edges of the rasterlines. It should be noted that the reason why the thinning ratio isincreased when approaching the edges is that, as noted above, thechances that ink droplets land on the paper S become lower toward theedges, so that the influence of thinning the ink droplets ejected towardthe vicinity of the edges is less prone to show up as empty portions inthe image. Consequently, it is possible to increase the number of inkdroplets that can be saved as much as possible, while suppressingdeterioration in the image quality due to thinning.

Moreover, it can be seen that when the change period Cm becomes large,there is less regularity in the thinned-out state, and the thinned-outstate tends to be better dispersed. Consequently, it is preferable thatthe change period Cm is set to be large, so that the empty portions inthe image that may become conspicuous at the edge of the paper S can bemade to be less readily apparent.

<Example of the Thinning Process for Overlap Printing>

FIGS. 24 through 31 show an example of the thinning process for the caseof overlap printing. In FIGS. 24 to 31, the change period Cm of thethin-out numbers is different in each drawing, thus illustrating theinfluence of the change period Cm on the thinned-out state. However, theconditions for overlap printing are set to the same conditions for allfigures. That is to say, the nozzle number N ejecting ink droplets isN=6, the nozzle pitch is k·D=4·D, the overlap number is M=2, and thecarry amount is F(=(N/M)·D)=3·D.

First, the raster line formation process with overlap printing isexplained with reference to FIG. 24. It should be noted that sinceoverlap printing has been explained before, only the aspects that arenecessary for the understanding of the present example are explainedhere.

Since the overlap number M of the present example is 2, ink droplets areejected from different nozzles in different passes onto the odd-numberedand the even-numbered pixels of the raster lines, forming the rasterlines.

For example, in the second pass, ink droplets are ejected by the nozzle#5 onto the even-numbered pixels of the second raster line R2, and inkdroplets are ejected by the nozzle #6 onto the even-numbered pixels ofthe sixth raster line R6, whereas the ink droplets for the odd-numberedpixels of these second and sixth raster lines R2 and R6 are ejected bythe nozzle #2 and the nozzle #3 in the sixth pass. Thus, the second andthe sixth raster lines R2 and R6 are completed.

Also, the third, fourth and fifth raster lines R3, R4 and R5 are formedas follows between the second raster line R2 and the sixth raster lineR6. In the third raster line R3, ink droplets are ejected onto theodd-numbered pixels by the nozzle #6 in the first pass, and the thirdraster line R3 is completed by ejecting ink droplets onto theeven-numbered pixels from the nozzle #3 in the fifth pass. In the fourthraster line R4, ink droplets are ejected onto the odd-numbered pixels bythe nozzle #1 in the eighth pass, and the fourth raster line R4 iscompleted by ejecting ink droplets onto the even-numbered pixels fromthe nozzle #4 in the fourth pass. In the fifth raster line R5, inkdroplets are ejected onto the odd-numbered pixels by the nozzle #5 inthe third pass, and the fifth raster line R5 is completed by ejectingink droplets onto the even-numbered pixels from the nozzle #2 in theseventh pass.

This means that, in order to consecutively form the second to sixthraster lines, a total of eight passes from the first pass to the eighthpass are necessary. In other words, in the overlap printing according tothe present example, eight passes form one cycle, and raster lines areformed consecutively at a dot pitch D in the carrying direction byrepeating this cycle. In the following this one cycle is referred to as“overlap cycle”, and in the figures, the first cycle is referred to as“i-th cycle”, whereas the next cycles is referred to as the “(i+1)-thcycle”. Moreover, the pass number Co constituting this one cycle iscalled the overlap cycle number Co.

The following is an explanation of the thinning process in theabandonment region Aa.

As shown in FIG. 24, an abandonment region Aa with a width of 32 pixelsin the ejection head movement direction is set to the right of thereference region Aa, and the edges of the raster lines are located atthe outer border of this abandonment region Aa. Moreover, in each pass,a thinning process based on the thin-out number corresponding to thatpass is performed, whereby a number of pixels corresponding to thethin-out number is counted from the edge of each raster line formed ineach pass and designated, and no ink droplets are ejected onto thedesignated pixels. It should be noted that to facilitate the drawings,the number of pixels in ejection head movement direction constitutingthe abandonment region has been set to 32, but there is no limitation tothis.

As shown below the left diagram in FIGS. 24 to 31, the change period Cmof the thin-out number is changed from two to nine passes from FIG. 24to FIG. 31, respectively. The change pattern of the thin-out number forthese examples is obtained by setting the value j in Table 2 to “4”. Forexample, in the case of FIG. 24 where the change period Cm is 2 passes,the thin-out number for each pass repeats the cycle of 0 and 4. Further,in the case of FIG. 25 where the change period Cm is 3 passes, thethin-out number repeats the cycle of 0, 4, and 16. As for the four tonine passes in FIGS. 26 to 31, every time the change period Cm increasesby one, one of the numbers 8, 0, 12, 16, and 0 is added in this order asthe thin-out number of the corresponding fourth and further passes.

This is explained taking FIG. 25, in which the change period Cm is 3passes, as a representative example of all figures. As shown below theleft diagram, the thin-out number changes at each pass in the order of 0dots-4 dots-16 dots. This change pattern is repeated for all passes ofthe overlap printing.

It should be noted that as mentioned above, in the case of overlapprinting with an overlap number M of 2, ink droplets can be ejected in asingle pass only onto either the odd-numbered pixels or theeven-numbered pixels lined up in the raster line direction.Consequently, the pixels that are thinned out in a single pass aredesignated by counting either the odd-numbered pixels or theeven-numbered pixels, from the edge of the raster line to the thin-outnumber corresponding to that pass. Moreover, the thinned-out state ofthe raster line is determined depending on which of the thin-out numberof the pass in which ink droplets are ejected onto even-numbered pixelsand the thin-out number of the pass in which ink droplets are ejectedonto odd-numbered pixels is larger. That is to say, this determineswhether intermittently-ejected portions are formed by ejecting inkdroplets onto every other pixel in the raster line direction, or whethera consecutive ejection portion is formed by ejecting consecutively inthat direction, or whether a consecutive non-ejection portion is formedin which no ink droplets are ejected consecutively in that direction.

For example, as shown in FIG. 25, the thin-out number of the first passof the i-th cycle is 0, so that there is no thinning of odd-numberedpixels of the third raster line R3, which are formed by the nozzle #6 ofthe first pass, and thus ink droplets are ejected by the nozzle #6 ontothe odd-numbered pixels of that raster line R3 all the way to the edgeof the raster line, as shown in the right diagram. On the other hand,ink droplets are ejected in a complementary manner by the nozzle #3 inthe fifth pass onto the even-numbered pixels between these odd-numberedpixels. At this time, the thin-out number of the fifth pass is 4, sothat no ink droplets are ejected onto a total of four even-numberedpixels counting from the edge of the raster line R3, but ink dropletsare ejected onto even-numbered pixels that are located further inward.As a result of these two passes, an intermittently-ejected portion inwhich ink droplets are ejected onto every other pixel is formed in aportion extending over eight pixels from the edge of the third rasterline R3, as shown in the right diagram, whereas a consecutive ejectionportion onto which ink droplets are ejected consecutively is formed in aportion extending over the 24 pixels further inward therefrom.

Also, as can be seen in the right diagram, there is a consecutivenon-ejection portion at the edge portion of the second raster line R2,and it is formed as follows. The thin-out number of the sixth pass ofthe i-th cycle is 16, so that no ink droplets are ejected onto a totalof 16 odd-numbered pixels counting from the edge of the raster line R2.As a result, no ink droplets are ejected onto any of the odd-numberedpixels of the raster line R2 in the abandonment region Aa. On the otherhand, the thin-out number of the second pass in this cycle is 4, so thatin this second pass, no ink droplets are ejected onto a total of foureven-numbered pixels counting from the edge of the raster line R2,whereas ink droplets are ejected by the nozzle #5 onto the even-numberedpixels that are located further inward. As a result, a consecutivenon-ejection portion onto which ink droplets are consecutively notejected is formed in a portion extending over eight pixels from the edgeof the second raster line R2, and an intermittently-ejected portion inwhich ink droplets are ejected onto every other pixel is formed in aportion extending over 24 pixels further inward therefrom, as shown inthe right diagram.

Also in the other raster lines besides the raster lines R2 and R3described above, whether an intermittently-ejected portion, aconsecutive ejection portion or a consecutive non-ejection portion isformed depends on which of the thin-out number of the pass in which inkdroplets are ejected toward the odd-numbered pixels and the thin-outnumber of the pass in which ink droplets are ejected toward theeven-numbered pixels is larger, as in these raster lines R2 and R3, andas a result, the thinned-out state of the raster lines is determined.

---Influence of the Change Period Cm on the Thinned-out State---

Referring to the FIGS. 24 to 31, the following is a discussion of theinfluence that the change period Cm has on the thinned-out state. Whatcan be seen immediately is that if intermittently-ejected portions areformed as shown in FIG. 25 and FIGS. 27 to 31, then the thinned-outstate looks dispersed, and in particular the greater theintermittently-ejected portions is, the more dispersed it looks.Conversely, if no intermittently-ejected portion is formed in any of theraster lines as shown in FIGS. 24 and 26, then the thinned-out statedoes not look dispersed, which is not preferable.

Accordingly, the conditions under which no intermittently-ejectedportions are formed at all, as in FIGS. 24 and 26, have been examined intwo steps. In the first step of this examination, the conditions underwhich no intermittently-ejected portion is formed in a predeterminedraster line were examined. In the second step, the conditions underwhich the conditions of the first step apply to all raster lines wereexamined.

First, the conclusion of the first step, namely the “conditions underwhich no intermittently-ejected portion is formed in a predeterminedraster line”, is as follows: This is the condition that “the pass forejecting droplets onto the even-numbered pixels of a raster line and thepass for ejecting droplets onto the odd-numbered pixels of that rasterline have the same thin-out number.” Or putting it more generally, thisis the condition that “the thin-out numbers of the pair of passes forforming the same raster line are the same.”

This is explained in more detail. The thin-out number stipulates thenumber of pixels that are thinned out, and at the same time alsostipulates the range from the edge of a raster line inward over whichpixels are thinned out. Consequently, if the thin-out numbercorresponding to the pass of the odd-numbered pixels is the same numberas the thin-out number corresponding to the pass of the even-numberedpixels, then the thinned out range matches, so that both are thinned outover the same range and no intermittently-ejected portion is formed.Conversely, if the thin-out numbers are different, then the thinned outranges are also different, so that in these different ranges there is aportion in which only the pixels of one type are thinned out and thepixels of the other type are not thinned out, thus forming anintermittently-ejected portion.

For example, in the nineteenth raster line R19 in the example in FIG.29, no intermittently-ejected portion is formed, because the thin-outnumber of the first pass in the (i+1)-th cycle, which is the pass of theodd-numbered pixels of the nineteenth raster line R19, is the samenumber, namely 4, as the thin-out number of the fifth pass in thatcycle, in which ink droplets are ejected onto the even-numbered pixelsof that raster line R19. That is to say, a thin-out number of 4 isassociated with both the first pass of the (i+1)-th cycle in which thereis ejection from the nozzle #4 toward the odd-numbered pixels of thefirst raster line R1, and the same thin-out number of 4 is associatedalso with the fifth pass in which there is of ejection from the nozzle#1 toward the even-numbered pixels. In this case, four odd-numberedpixels as well as four even-numbered pixels are designated. Thus, thethinning range of the even-numbered pixels and the odd-numbered pixelsextends for eight pixels from the edge of the raster line. Consequently,in a range of eight pixels from the edge, both the odd-numbered and theeven-numbered pixels are thinned out, thus forming a consecutivenon-ejection portion, whereas in the range further inward, neither theodd-numbered and the even-numbered pixels are thinned out, forming aconsecutive ejection portion. As a result, no intermittently-ejectedportion is formed in this first raster line R1.

On the other hand, the first raster line R1, which includes anintermittently-ejected portion, is formed as follows. The third pass, inwhich there is ejection from the nozzle #4 toward the odd-numberedpixels of the first raster line R1, is associated with the thin-outnumber 16, whereas the seventh pass, in which there is ejection from thenozzle #1 toward the even-numbered pixels, is associated with thethin-out number 8. Thus, in this case, 16 odd-numbered pixels (i.e.every other pixel) are designated, and as a result the thinned out rangeextends over 32 pixels from the edge of the raster line. On the otherhand, 8 even-numbered pixels (i.e. every other pixel) are designated,and as a result the thinned out range extends over 16 pixels from theedge of the raster line. Consequently, both odd-numbered andeven-numbered pixels are thinned out in a range of 16 pixels from theedge, thus forming a consecutive non-ejection portion, whereas in therange further inward, only odd-numbered pixels are thinned out, so thatan intermittently-ejected portion is formed as a result.

The following is a discussion of the second step regarding “theconditions under which the conditions of the first step apply to allraster lines” are examined. That is to say, the “conditions under whichthe thin-out numbers of the pair of passes for forming the same rasterline are the same in all raster lines” are examined.

The conclusion is as follows: This is the condition that “the quotientCo/M of the overlap cycle number Co divided by the overlap number M is amultiple (i.e. an integer other than 1) of the change period Cm of thethin-out numbers.”

This is explained in more detail. Ordinarily, the two pass numbers forforming the same raster line are spaced apart by a pass number that canbe expressed as the quotient Co/M of the overlap cycle number Co dividedby the overlap number M. In the present example, Co/M=8/2, so that theyare spaced apart by four passes. For example, as shown in the leftdiagram of FIG. 26, the pair of passes for forming the third raster lineR3 are the first pass and the fifth pass, the pair of passes for formingthe second raster line are the second pass and the sixth pass, and thepair of passes for forming the first raster line are the third pass andthe seventh pass, so that those passes are respectively spaced apart byfour passes. Moreover, this relation is true for all passes.

Therefore, when this interval of passes is a multiple of the changeperiod Cm of the thin-out numbers, then both of the passes willinevitably be associated with the same thin-out number, so that therewill be no intermittently-ejected portion in any of the raster lines.

For example, in the example in the figure, the change period Cm is fourpasses, which means that the same thin-out numbers are repeated everyfour passes. Moreover, also the interval of the pair of passes formingthe same raster line is four passes, so that passes forming a pair willinevitably correspond to the same thin-out number. That is to say, thefirst pass and the fifth pass for forming the third raster line R3 areboth associated with the thin-out number 0, the second pass and thesixth pass for forming the second raster line R2 are both associatedwith the thin-out number 4, and the third pass and the seventh pass forforming the first raster line R1 are both associated with the thin-outnumber 16. And since this relation is true for all raster lines, nointermittently-ejected portion is formed in the whole abandonment regionAa, as shown in the right diagram.

Note that, in the examples of FIGS. 24 through 31 used to illustratedoverlap printing, the change period Cm corresponding to this relation istwo passes in FIG. 24 and four passes in FIG. 26, and nointermittently-ejected portion is formed in the abandonment region Aa inneither of them. It should be noted that the value of Co/M is the sameas the value of k mentioned above.

Note further that the above-stated condition is the condition that nointermittently-ejected portion is formed at all. Therefore, thepreferable condition is the opposite condition in whichintermittently-ejected portions are formed: “the quotient Co/M of theoverlap cycle number Co divided by the overlap number M is not amultiple (an integer other than 1) of the change period Cm of thethin-out numbers.” It is preferable that Co, Cm and M are selected suchthat this condition is satisfied.

It is even more preferable that the following condition is satisfied:“the overlap cycle Co is coprime to the change period Cm of the thin-outnumbers.” In this case, the above-noted condition that“intermittently-ejected portions are formed” is of course satisfied, andit can be ensured that the overlap cycle number Co and the change periodCm of the thin-out numbers differ. Consequently, it is possible to makethe periodicity of the thinned-out state in the carrying direction moreintricate, and thus empty portions in the image, when the thinned-outstate appears at the edges of the medium, can be made even lessconspicuous.

---Regarding the Preferable Dot Shape Formed by Ink Droplets---

The following is an explanation of the preferable dot shape formed bythe ink droplets. The dot shape of the ink droplets is the shape thatremains after the ink droplets have landed on the paper S. It ispreferable that this shape is substantially that of an ellipse whosemajor axis is oriented in the raster line direction. The reason for thisis that, in the above-noted intermittently-ejected portion, blankportions are formed at every other pixel in the raster line direction,but if the dot shape is substantially elliptical, then these blankportions tend to be filled up, so that it is possible to make theseblank portions non-conspicuous.

===Discussion of Preferable Change Patterns===

With the goal of finding preferable examples of change patterns as shownin Table 2 above, the change of the thinned-out state was examined forvarious different change patterns as shown in Table 3. It should benoted that the print mode is overlap printing with the conditions listedin Table 4. TABLE 3 first second third fourth fifth sixth seventh eighthninth pass pass pass pass pass pass pass pass pass pass thin- changepattern 1 0 8  0 16  0 24  0 — — out (change period number of 7 passes)(pixels) change pattern 2 0 8  0 16  0 24  0 32 0 (change period of 9passes) change pattern 3 0 8 16 24 32 24 16  8 0 (change period of 9passes) change pattern 4 0 8 32 16  0 24  0 32 0 (change period of 9passes) change pattern 5 0 8 32 16  0 24 16 32 0 (change period of 9passes)

TABLE 4 carry nozzle pitch nozzle number N amount (=k · D) ejecting inkdroplets F overlap number M 16 · D 90 43 · D 2 or 3 (1 out of 16 rasterlines has M = 3)

FIGS. 32 through 36 are plan views showing the thinned-out state in theabandonment region Aa. It should be noted that these diagrams are drawnin the same form as the right diagrams in FIGS. 16 through 31. However,the pixels onto which ink droplets are ejected are shown in black, andconversely the pixels onto which no ink droplets are ejected are shownin white.

Firstly, the overlap printing used for this discussion is outlined. Whenoverlap printing is performed in accordance with the overlap conditionsin Table 4, one out of every sixteen raster lines is formed with anoverlap number of 3, and the remaining fifteen of the sixteen rasterlines are formed with an overlap number of 2. That is to say, one rasterline is formed by ejecting ink droplets onto the pixels alternately fromthree nozzles, whereas fifteen raster lines are formed by ejecting inkdroplets onto the pixels alternately from two nozzles.

As shown in FIG. 32, the abandonment region Aa is set to a width of 56pixels in the ejection head movement direction, and the edges of theraster lines are located at the outer border of this abandonment regionAa. Note that in FIGS. 33 through 36, in a portion in the carryingdirection, the pixels onto which no ink droplets are ejected reach allthe way to the inner side of the reference region; these raster linesare formed in passes associated with a thin-out number of 32. That is tosay, the overlap number of these raster lines is 2, so that if thethin-out number is 32, then there are a maximum of 64 pixels from theedge of the raster line in which the pixels on the inner side arethinned out.

Here, in the FIGS. 32 through 36, the change patterns 1 through 5 allhave a large intermittently-ejected portion, and there is a lot ofvariation in the thinned-out state, which is preferable. However, sincethe thinned-out state of the change pattern 5 looks the most varied, itseems to be the most preferable. When this change pattern 5 isgeneralized, it can be expressed as in the above-noted Table 2. In otherwords, if the value j of the change pattern in Table 2 is set to “4”,then it becomes the change pattern 5.

Other Embodiments

In the foregoing, the liquid ejection apparatus of this embodiment wasdescribed taking an inkjet printer as an example. However, the foregoingembodiment is for the purpose of elucidating the present invention andis not to be interpreted as limiting the present invention. Theinvention can of course be altered and improved without departing fromthe gist thereof and includes equivalents. In particular, theembodiments described below are also included in the liquid ejectionapparatus according to the present invention.

In embodiments of the present invention, some or all of theconfigurations achieved by hardware may be replaced by software, andconversely, some of the configurations that are achieved by software canbe replaced by hardware.

The medium also may be cloth and film, for example, instead of the printpaper S.

It is possible to perform some of the processes that are performed onthe liquid ejection apparatus side on the host side instead, and it isalso possible to provide a dedicated processing device between theliquid ejection apparatus and the host and perform some of the processesusing this processing device.

Moreover, in the embodiments of the present invention, in order toperform borderless printing, the abandonment region Aa that isdetermined to be outside the print paper S is set outside the paper Sand ink droplets are thinned out with respect to this region Aa, asshown in FIG. 11. However, there is no limitation to this.

For example, by setting the print region A in FIG. 11 to substantiallythe same size as the paper S, the invention can also be adopted for acase in which borderless printing is performed without providing anabandonment region Aa. That is, if the position of the paper S does notdeviate from a set design position when the paper is carried, then allthe ink droplets land on the paper S without any ink droplets beingabandoned, but if its position has deviated, then there are ink dropletsthat miss the paper S without landing on it, and these droplets areabandoned. In this case, it is also possible to thin out a suitablenumber of ink droplets that are abandoned at this time. It should benoted that in this case, ink droplets that are ejected toward portionsmore inward than the edges of the paper S will be thinned out, but thisconcept is also encompassed within the scope of the invention accordingto claim 1. That is to say, the concept of “toward the vicinity of theedge of the medium” in claim 1 includes both the inner side and theouter side of the medium (the paper S).

Also, embodiments of the present invention were explained in detail forthe case that the thinning process is performed at the lateral edges ofthe print paper S, but needless to say, it can also be performed at theupper and lower edges of the print paper S.

Moreover, in the embodiments of the present invention, the thinningprocessing section 224 is provided in the drive circuit inside the headdriver 22, but there is no limitation to this. For example, it is alsopossible to provide a module for performing the thinning process insidethe printer driver 96, and to perform the thinning process on the printdata PD that is transferred from the rasterizer 100. It should be notedthat in this case, the thinning signal SIG will already be reflected inthe print signals PRT(i) of the print data that has been subjected tothe thinning process by this module, so that there is no need to inputthe thinning signal SIG into the mask circuit 222 in the drive circuit,as in the above-described embodiments.

<Regarding the Liquid Ejection Apparatus>

The liquid ejection apparatus of the present invention can be adoptedfor printing apparatuses such as an inkjet printer as described above,and in addition to these it also can be adopted for color filtermanufacturing devices, dyeing devices, fine processing devices,semiconductor manufacturing devices, surface processing devices,three-dimensional shape forming machines, liquid vaporizing devices,organic EL manufacturing devices (particularly macromolecular ELmanufacturing devices), display manufacturing devices, film formationdevices, and DNA chip manufacturing devices, for example.

<Regarding the Liquid>

The liquid of the present invention is not limited to inks, such as dyeink or pigment ink, as described above, and it is also possible to adoptliquids (including water) including metallic material, organic material(particularly macromolecular material), magnetic material, conductivematerial, wiring material, film-formation material, electric ink,processed liquid, and genetic solutions, for example. Moreover, asregards the constituents of the liquid, the liquid can also be made ofsolvents such as water and dissolving agents.

<Regarding the Medium>

As for the medium, it is possible to use regular paper, matte paper, cutpaper, glossy paper, roll paper, paper used for a specific purpose,photographic paper, and rolled photographic paper, for example, as thepaper S described above. In addition to these, it is also possible touse film material such as OHP film or glossy film, cloth material, andsheet metal material, for example. In other words, any medium may beused, as long as liquid can be ejected onto it.

<Regarding the Nozzle Rows>

The nozzle rows provided in the ejection head are not limited to theabove-described four rows of black (K), cyan (C), magenta (M), andyellow (Y), and it is also possible to provide nozzle rows for ejectingink of other colors than these. For example, a nozzle row for ejectingclear ink, which is transparent ink, may also be provided.

<Regarding the Change of the Thin-Nut number in Each Pass>

As for the change of the thin-out number in each pass, there is nolimitation to changing the thin-out number in accordance with apredetermined change pattern as explained above, and it is also possibleto associate random numbers generated by a random number generator witheach pass, and to change the thin-out number in accordance with theserandom numbers.

INDUSTRIAL APPLICABILITY

According to the present invention, a liquid ejection apparatus and aliquid ejection method are achieved with which the number of liquiddroplets ejected onto a region outside the medium, which becomes anecessary evil when forming dots all the way to the edges of the mediumby ejecting ink droplets, can be decreased without greatly impairing theformation of dots at the edges.

1. A liquid ejection apparatus for ejecting a liquid, comprising: aliquid ejection section for ejecting liquid droplets toward a medium inorder to form dots on said medium; wherein said liquid ejection sectionejects, toward a vicinity of an edge of said medium, said liquiddroplets of a number that has been thinned out by a suitable number; andwherein at least a portion of the liquid droplets ejected after thinningdoes not land on said medium.
 2. A liquid ejection apparatus accordingto claim 1, wherein, when ejecting said liquid droplets from said liquidejection section toward a region that is determined to be outside saidmedium, said liquid droplets are ejected after thinning a suitablenumber of the liquid droplets that are to be ejected toward that region.3. A liquid ejection apparatus according to claim 2, wherein said liquiddroplets are ejected based on image data formed to a size that is largerthan said medium, and a reference region corresponding to the size ofsaid medium is stored; and wherein the region that is determined to beoutside said medium is a region that is outside said reference region.4. A liquid ejection apparatus according to claim 3, wherein said liquidejection section comprises nozzles ejecting said liquid droplets;wherein an image formed on said medium based on said image data isconstituted by raster lines that are arranged in parallel to one anotherat a predetermined interval in a direction intersecting the direction ofsaid raster lines, each of said raster lines being made of a multitudeof dots arranged on a straight line; and wherein said raster lines areformed by ejecting said liquid droplets while moving said nozzles in theraster line direction.
 5. A liquid ejection apparatus according to claim4, wherein a ratio at which said liquid droplets are thinned out in theregion that is determined to be outside said medium increases toward theedge in said raster line direction.
 6. A liquid ejection apparatusaccording to claim 4, wherein said nozzles constitute a nozzle row inwhich said nozzles are arranged at a predetermined nozzle pitch in adirection intersecting with said raster line direction; wherein saidmedium is intermittently carried by a predetermined carry amount in saidintersecting direction; and wherein, in between the intermittentcarries, said nozzle row forms the raster lines while moving in saidraster line direction.
 7. A liquid ejection apparatus according to claim6, wherein, for a single movement operation of said nozzle row in saidraster line direction, the liquid droplets are thinned out by apredetermined thin-out number consecutively from the edge in said rasterline direction and said thin-out number is the same number for all ofthe nozzles constituting said nozzle row; and wherein said thin-outnumber is changed for every said movement operation of said nozzle row.8. A liquid ejection apparatus according to claim 7, wherein saidthin-out number of the liquid droplets is changed for every saidmovement operation based on a predetermined change pattern, and thethin-out numbers based on this change pattern form a cycle that makes around every time a predetermined number Cm of said movement operationsare repeated.
 9. A liquid ejection apparatus according to claim 6,wherein said nozzle pitch of said nozzle row is wider than the intervalbetween the raster lines formed on said medium; and wherein there is anunformed raster line between raster lines that are formed by said nozzlerow in a single movement operation in said raster line direction.
 10. Aliquid ejection apparatus according to claim 9, wherein, when theinterval between the raster lines formed on said medium is D, saidnozzle pitch is k·D, the number of said nozzles ejecting said liquid isN, and said carry amount is F, then: N is coprime with k; and F=N·D. 11.A liquid ejection apparatus according to claim 9, wherein each of saidraster lines formed on said medium is formed using a plurality ofnozzles.
 12. A liquid ejection apparatus according to claim 11, whereinsaid raster line includes an intermittently-ejected portion that isformed by ejecting the liquid droplets after performing intermittentthinning.
 13. A liquid ejection apparatus according to claim 12, whereina predetermined number Co of movement operations of said nozzle row isrequired to form raster lines at said interval D on said medium; andwherein said predetermined number Co is coprime to said predeterminednumber Cm regarding the change pattern of said thin-out numbers.
 14. Aliquid ejection apparatus according to claim 11, wherein, when eachraster line is formed by M nozzles, and when the interval between theraster lines formed on said medium and the interval between the dots insaid raster line direction are both D, said nozzle pitch is k·D, thenumber of said nozzles ejecting said liquid droplets is N, and saidcarry amount is F, then: N/M is an integer; N/M is coprime to k; andF=(N/M)·D.
 15. A liquid ejection apparatus according to claim 14,wherein said k is not a multiple (an integer multiple other than 1) ofsaid predetermined number Cm.
 16. A liquid ejection apparatus accordingto claim 12, wherein the shape of said dots is substantially the shapeof an ellipse whose major axis is oriented in said raster linedirection.
 17. A liquid ejection apparatus according to claim 2, whereinsaid liquid ejection apparatus further comprises an input section intowhich a command is input that indicates whether or not to eject theliquid droplets after thinning; and wherein, if a command to eject theliquid droplets after thinning is input, then said liquid droplets areejected after thinning a suitable number of the liquid droplets that areto be ejected toward said region.
 18. A liquid ejection apparatus forejecting a liquid, comprising: a liquid ejection section for ejectingliquid droplets toward a medium in order to form dots on said medium;wherein a mode for ejecting the liquid droplets without forming a marginat an edge of said medium can be set; and wherein, if said mode has beenset, then: said liquid ejection section ejects, toward a vicinity ofsaid edge of said medium, said liquid droplets of a number that has beenthinned out by a suitable number; and at least a portion of the liquiddroplets ejected after thinning does not land on said medium.
 19. Aliquid ejection apparatus for ejecting a liquid, comprising: a liquidejection section for ejecting liquid droplets toward a medium in orderto form dots on said medium; and an input section into which a commandis input that indicates whether or not to eject the liquid dropletsafter thinning; wherein, if a command to eject the liquid droplets afterthinning is input, then when ejecting said liquid droplets from saidliquid ejection section toward a region that is determined to be outsidesaid medium, said liquid droplets are ejected after thinning a suitablenumber of the liquid droplets that are to be ejected toward that region;wherein said liquid droplets are ejected based on image data formed to asize that is larger than said medium, a reference region correspondingto the size of said medium is stored, and the region that is determinedto be outside said medium is a region that is outside said referenceregion; wherein said liquid ejection section comprises nozzles ejectingsaid liquid droplets; wherein an image formed on said medium based onsaid image data is constituted by raster lines that are arranged inparallel to one another at a predetermined interval in a directionintersecting the direction of said raster lines, each of said rasterlines being made of a multitude of dots arranged on a straight line;wherein said raster lines are formed by ejecting said liquid dropletswhile moving said nozzles in the raster line direction; wherein a ratioat which said liquid droplets are thinned out in the region that isdetermined to be outside said medium increases toward the edge in saidraster line direction; wherein said nozzles constitute a nozzle row inwhich said nozzles are arranged at a predetermined nozzle pitch in adirection intersecting with said raster line direction; wherein saidmedium is intermittently carried by a predetermined carry amount in saidintersecting direction; wherein, in between the intermittent carries,said nozzle row forms the raster lines while moving in said raster linedirection; wherein said nozzle pitch of said nozzle row is wider thanthe interval between the raster lines formed on said medium; whereinthere is an unformed raster line between raster lines that are formed bysaid nozzle row in a single movement operation in said raster linedirection; wherein each of said raster lines formed on said medium isformed using a plurality of nozzles; wherein, for a single movementoperation of said nozzle row in said raster line direction, the liquiddroplets are thinned out by a predetermined thin-out numberconsecutively from the edge in said raster line direction and saidthin-out number is the same number for all of the nozzles constitutingsaid nozzle row; wherein said thin-out number is changed for every saidmovement operation of said nozzle row; wherein said thin-out number ofthe liquid droplets is changed for every said movement operation basedon a predetermined change pattern, and the thin-out numbers based onthis change pattern form a cycle that makes a round every time apredetermined number Cm of said movement operations are repeated;wherein a predetermined number Co of movement operations of said nozzlerow is required to form raster lines at said interval D on said medium;and wherein said predetermined number Co is coprime to saidpredetermined number Cm regarding the change pattern of said thin-outnumbers.
 20. A liquid ejection method for ejecting liquid dropletstoward a medium in order to form dots on said medium, said methodcomprising: a step of thinning out a suitable number of liquid dropletsto be ejected; and a step of ejecting, toward a vicinity of an edge ofsaid medium, said liquid droplets of a number that has been thinned outby said suitable number; wherein at least a portion of the liquiddroplets ejected after thinning does not land on said medium.
 21. Aliquid ejection apparatus according to claim 5, wherein said nozzlesconstitute a nozzle row in which said nozzles are arranged at apredetermined nozzle pitch in a direction intersecting with said rasterline direction; wherein said medium is intermittently carried by apredetermined carry amount in said intersecting direction; and wherein,in between the intermittent carries, said nozzle row forms the rasterlines while moving in said raster line direction.
 22. A liquid ejectionapparatus according to claim 21, wherein, for a single movementoperation of said nozzle row in said raster line direction, the liquiddroplets are thinned out by a predetermined thin-out numberconsecutively from the edge in said raster line direction and saidthin-out number is the same number for all of the nozzles constitutingsaid nozzle row; and wherein said thin-out number is changed for everysaid movement operation of said nozzle row.
 23. A liquid ejectionapparatus according to claim 22, wherein said thin-out number of theliquid droplets is changed for every said movement operation based on apredetermined change pattern, and the thin-out numbers based on thischange pattern form a cycle that makes a round every time apredetermined number Cm of said movement operations are repeated.
 24. Aliquid ejection apparatus according to claim 21, wherein said nozzlepitch of said nozzle row is wider than the interval between the rasterlines formed on said medium; and wherein there is an unformed rasterline between raster lines that are formed by said nozzle row in a singlemovement operation in said raster line direction.
 25. A liquid ejectionapparatus according to claim 24, wherein, when the interval between theraster lines formed on said medium is D, said nozzle pitch is k·D, thenumber of said nozzles ejecting said liquid is N, and said carry amountis F, then: N is coprime with k; and F=N·D.
 26. A liquid ejectionapparatus according to claim 24, wherein each of said raster linesformed on said medium is formed using a plurality of nozzles.
 27. Aliquid ejection apparatus according to claim 26, wherein said rasterline includes an intermittently-ejected portion that is formed byejecting the liquid droplets after performing intermittent thinning. 28.A liquid ejection apparatus according to claim 27, wherein apredetermined number Co of movement operations of said nozzle row isrequired to form raster lines at said interval D on said medium; andwherein said predetermined number Co is coprime to said predeterminednumber Cm regarding the change pattern of said thin-out numbers.
 29. Aliquid ejection apparatus according to claim 26, wherein, when eachraster line is formed by M nozzles, and when the interval between theraster lines formed on said medium and the interval between the dots insaid raster line direction are both D, said nozzle pitch is k·D, thenumber of said nozzles ejecting said liquid droplets is N, and saidcarry amount is F, then: N/M is an integer; N/M is coprime to k; andF=(N/M)·D.
 30. A liquid ejection apparatus according to claim 29,wherein said k is not a multiple (an integer multiple other than 1) ofsaid predetermined number Cm.
 31. A liquid ejection apparatus accordingto claim 27, wherein the shape of said dots is substantially the shapeof an ellipse whose major axis is oriented in said raster linedirection.